Added automatic version prefixing to releases

The script itself is a part of .travis.yml, using ./scripts/prefix.py
for applying prefixes to the source code.

This purpose of the automatic job is to provide a branch containing
version prefixes, to avoid name conflicts in binaries containing
different major versions of littlefs with only a git clone.

As a part of each release, two branches and a tag are created:
- vN        - moving branch
- vN-prefix - moving branch
- vN.N.N    - immutable tag

The major version branch (vM) is created on major releases, but updated
every patch release. The patch version tag (vM.M.P) is created every
patch release. Patch releases occur every time a commit is merged into
master, though multiple merges may be coalesced.

The major prefix branch (vM-prefix) is modified with the ./scripts/prefix.py
script. Note that this branch is updated as a synthetic merge commit
with the previous history of vM-prefix. The reason for this is to allow
users to easily update vM-prefix with a `git pull` as they would for
other branches.

A---B---C---D---E master, v1, v1.7.3
     \       \   \
      F-------G---H v1-prefix

.travis.yml

@@ -35,7 +35,7 @@ script:
     if [ "$TRAVIS_TEST_RESULT" -eq 0 ]
     then
         CURR=$(tail -n1 sizes | awk '{print $1}')
-        PREV=$(curl -u $GEKY_BOT_STATUSES https://api.github.com/repos/$TRAVIS_REPO_SLUG/status/master \
+        PREV=$(curl -u "$GEKY_BOT_STATUSES" https://api.github.com/repos/$TRAVIS_REPO_SLUG/status/master \
             | jq -re "select(.sha != \"$TRAVIS_COMMIT\")
                 | .statuses[] | select(.context == \"$STAGE/$NAME\").description
                 | capture(\"code size is (?<size>[0-9]+)\").size" \
@@ -100,6 +100,7 @@ jobs:
       env:
         - STAGE=test
         - NAME=littlefs-fuse
+      if: branch !~ -prefix$
       install:
         - sudo apt-get install libfuse-dev
         - git clone --depth 1 https://github.com/geky/littlefs-fuse
@@ -128,70 +129,88 @@ jobs:
         - ls
         - make -B test_dirs test_files QUIET=1
 
-      # Automatically update releases
+    # Automatically create releases
     - stage: deploy
       env:
         - STAGE=deploy
         - NAME=deploy
       script:
-        # Find version defined in lfs.h
-        - LFS_VERSION=$(grep -ox '#define LFS_VERSION .*' lfs.h | cut -d ' ' -f3)
-        - LFS_VERSION_MAJOR=$((0xffff & ($LFS_VERSION >> 16)))
-        - LFS_VERSION_MINOR=$((0xffff & ($LFS_VERSION >>  0)))
-        # Grab latests patch from repo tags, default to 0, needs finagling to get past github's pagination api
-        - PREV_URL=https://api.github.com/repos/$TRAVIS_REPO_SLUG/git/refs/tags/v$LFS_VERSION_MAJOR.$LFS_VERSION_MINOR.
-        - PREV_URL=$(curl -u "$GEKY_BOT_RELEASES" "$PREV_URL" -I
-                | sed -n '/^Link/{s/.*<\(.*\)>; rel="last"/\1/;p;q0};$q1'
-                || echo $PREV_URL)
-        - LFS_VERSION_PATCH=$(curl -u "$GEKY_BOT_RELEASES" "$PREV_URL"
-                | jq 'map(.ref | match("\\bv.*\\..*\\.(.*)$";"g")
-                    .captures[].string | tonumber) | max + 1'
-                || echo 0)
-        # We have our new version
-        - LFS_VERSION="v$LFS_VERSION_MAJOR.$LFS_VERSION_MINOR.$LFS_VERSION_PATCH"
-        - echo "VERSION $LFS_VERSION"
         - |
+          bash << 'SCRIPT'
+          set -ev
+          # Find version defined in lfs.h
+          LFS_VERSION=$(grep -ox '#define LFS_VERSION .*' lfs.h | cut -d ' ' -f3)
+          LFS_VERSION_MAJOR=$((0xffff & ($LFS_VERSION >> 16)))
+          LFS_VERSION_MINOR=$((0xffff & ($LFS_VERSION >>  0)))
+          # Grab latests patch from repo tags, default to 0, needs finagling
+          # to get past github's pagination api
+          PREV_URL=https://api.github.com/repos/$TRAVIS_REPO_SLUG/git/refs/tags/v$LFS_VERSION_MAJOR.$LFS_VERSION_MINOR.
+          PREV_URL=$(curl -u "$GEKY_BOT_RELEASES" "$PREV_URL" -I \
+              | sed -n '/^Link/{s/.*<\(.*\)>; rel="last"/\1/;p;q0};$q1' \
+              || echo $PREV_URL)
+          LFS_VERSION_PATCH=$(curl -u "$GEKY_BOT_RELEASES" "$PREV_URL" \
+              | jq 'map(.ref | match("\\bv.*\\..*\\.(.*)$";"g")
+                  .captures[].string | tonumber) | max + 1' \
+              || echo 0)
+          # We have our new version
+          LFS_VERSION="v$LFS_VERSION_MAJOR.$LFS_VERSION_MINOR.$LFS_VERSION_PATCH"
+          echo "VERSION $LFS_VERSION"
           # Check that we're the most recent commit
           CURRENT_COMMIT=$(curl -f -u "$GEKY_BOT_RELEASES" \
-                https://api.github.com/repos/$TRAVIS_REPO_SLUG/commits/master \
-                | jq -re '.sha')
-          if [ "$TRAVIS_COMMIT" == "$CURRENT_COMMIT" ]
+              https://api.github.com/repos/$TRAVIS_REPO_SLUG/commits/master \
+              | jq -re '.sha')
+          [ "$TRAVIS_COMMIT" == "$CURRENT_COMMIT" ] || exit 0
+          # Create major branch
+          git branch v$LFS_VERSION_MAJOR HEAD
+          # Create major prefix branch
+          git config user.name "geky bot"
+          git config user.email "bot@geky.net"
+          git fetch https://github.com/$TRAVIS_REPO_SLUG.git \
+              --depth=50 v$LFS_VERSION_MAJOR-prefix || true
+          ./scripts/prefix.py lfs$LFS_VERSION_MAJOR
+          git branch v$LFS_VERSION_MAJOR-prefix $( \
+              git commit-tree $(git write-tree) \
+                  $(git rev-parse --verify -q FETCH_HEAD | sed -e 's/^/-p /') \
+                  -p HEAD \
+                  -m "Generated v$LFS_VERSION_MAJOR prefixes")
+          git reset --hard
+          # Update major version branches (vN and vN-prefix)
+          git push https://$GEKY_BOT_RELEASES@github.com/$TRAVIS_REPO_SLUG.git \
+              v$LFS_VERSION_MAJOR \
+              v$LFS_VERSION_MAJOR-prefix
+          # Create patch version tag (vN.N.N)
+          curl -f -u "$GEKY_BOT_RELEASES" -X POST \
+              https://api.github.com/repos/$TRAVIS_REPO_SLUG/git/refs \
+              -d "{
+                  \"ref\": \"refs/tags/$LFS_VERSION\",
+                  \"sha\": \"$TRAVIS_COMMIT\"
+              }"
+          # Create minor release?
+          [[ "$LFS_VERSION" == *.0 ]] || exit 0
+          # Build release notes
+          PREV=$(git tag --sort=-v:refname -l "v*.0" | head -1)
+          if [ ! -z "$PREV" ]
           then
-            # Create a simple tag
-            curl -f -u "$GEKY_BOT_RELEASES" -X POST \
-                https://api.github.com/repos/$TRAVIS_REPO_SLUG/git/refs \
-                -d "{
-                    \"ref\": \"refs/tags/$LFS_VERSION\",
-                    \"sha\": \"$TRAVIS_COMMIT\"
-                }"
-            # Minor release?
-            if [[ "$LFS_VERSION" == *.0 ]]
-            then
-              # Build release notes
-              PREV=$(git tag --sort=-v:refname -l "v*.0" | head -1)
-              if [ ! -z "$PREV" ]
-              then
-                  echo "PREV $PREV"
-                  CHANGES=$'### Changes\n\n'$( \
-                      git log --oneline $PREV.. --grep='^Merge' --invert-grep)
-                  printf "CHANGES\n%s\n\n" "$CHANGES"
-              fi
-              # Create the release
-              curl -f -u "$GEKY_BOT_RELEASES" -X POST \
-                  https://api.github.com/repos/$TRAVIS_REPO_SLUG/releases \
-                  -d "{
-                      \"tag_name\": \"$LFS_VERSION\",
-                      \"name\": \"${LFS_VERSION%.0}\",
-                      \"draft\": true,
-                      \"body\": $(jq -sR '.' <<< "$CHANGES")
-                  }"
-            fi
+              echo "PREV $PREV"
+              CHANGES=$'### Changes\n\n'$( \
+                  git log --oneline $PREV.. --grep='^Merge' --invert-grep)
+              printf "CHANGES\n%s\n\n" "$CHANGES"
           fi
+          # Create the release
+          curl -f -u "$GEKY_BOT_RELEASES" -X POST \
+              https://api.github.com/repos/$TRAVIS_REPO_SLUG/releases \
+              -d "{
+                  \"tag_name\": \"$LFS_VERSION\",
+                  \"name\": \"${LFS_VERSION%.0}\",
+                  \"draft\": true,
+                  \"body\": $(jq -sR '.' <<< "$CHANGES")
+              }" #"
+          SCRIPT
 
 # Manage statuses
 before_install:
   - |
-    curl -u $GEKY_BOT_STATUSES -X POST \
+    curl -u "$GEKY_BOT_STATUSES" -X POST \
         https://api.github.com/repos/$TRAVIS_REPO_SLUG/statuses/${TRAVIS_PULL_REQUEST_SHA:-$TRAVIS_COMMIT} \
         -d "{
             \"context\": \"$STAGE/$NAME\",
@@ -202,7 +221,7 @@ before_install:
 
 after_failure:
   - |
-    curl -u $GEKY_BOT_STATUSES -X POST \
+    curl -u "$GEKY_BOT_STATUSES" -X POST \
         https://api.github.com/repos/$TRAVIS_REPO_SLUG/statuses/${TRAVIS_PULL_REQUEST_SHA:-$TRAVIS_COMMIT} \
         -d "{
             \"context\": \"$STAGE/$NAME\",
@@ -213,7 +232,7 @@ after_failure:
 
 after_success:
   - |
-    curl -u $GEKY_BOT_STATUSES -X POST \
+    curl -u "$GEKY_BOT_STATUSES" -X POST \
         https://api.github.com/repos/$TRAVIS_REPO_SLUG/statuses/${TRAVIS_PULL_REQUEST_SHA:-$TRAVIS_COMMIT} \
         -d "{
             \"context\": \"$STAGE/$NAME\",