Add changelog generation workflow to github actions

.github/workflows/changelog.yaml

@@ -0,0 +1,82 @@
+name: Changelog
+
+on:
+  push:
+    branches: [ develop ]
+
+jobs:
+  generate:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Check branch for new commits
+        run: |
+          git fetch origin
+          BRANCH="${GITHUB_REF##*/}"
+          if [[ $(git rev-parse "origin/$BRANCH") != $GITHUB_SHA ]]; then
+            echo "BRANCH: $BRANCH"
+            echo "GITHUB_SHA: $GITHUB_SHA"
+            echo "$BRANCH has been updated since build started. Aborting changelog."
+            exit 1
+          fi
+          echo "BRANCH=$BRANCH" >> $GITHUB_ENV
+
+      - name: Prep environment variables
+        run: |
+          echo "BRANCH=${GITHUB_REF##*/}" >> $GITHUB_ENV
+          echo "FILENAME=CHANGELOG.md" >> $GITHUB_ENV
+          echo "gittag=$(git tag --sort=-creatordate | grep -Ev '(alpha|beta|rc)' | awk 'NR==1')" >> $GITHUB_ENV
+
+      - name: Prep changelog file (clear out old lines)
+        run: |
+          # delete the top of the changelog up to the correct tag
+          tagline=$(grep -n "^## \[\?$gittag\]\?" "$FILENAME" | awk '{print $1}' FS=':' | head -1)
+          echo "tagline: ${tagline}"
+          [[ ! -z $tagline ]] && sed -i "1,$(expr $tagline - 1)d" "$FILENAME"
+          # delete generated line (or it will be added multiple times)
+          sed -i '/This Changelog was automatically generated by/d' "$FILENAME"
+          # delete trailing empty lines
+          sed -i -e :a -e '/^\n*$/{$d;N;};/\n$/ba' "$FILENAME"
+
+      - name: Generate changelog
+        uses: heinrichreimer/action-github-changelog-generator@v2.1.1
+        with:
+          # see: https://github.com/heinrichreimer/action-github-changelog-generator
+          repo: jrnl-org/jrnl
+          token: ${{ secrets.GITHUB_TOKEN }}
+          base: CHANGELOG.md
+          addSections: '{"build":{"prefix":"**Build:**","labels":["build"]},"docs":{"prefix":"**Documentation:**","labels":["documentation"]}}'
+          issues: true
+          issuesWoLabels: false
+          unreleased: true
+          compareLink: true
+          includeLabels: bug,enhancement,documentation,build,deprecated
+          excludeLabels: stale,wontfix
+          excludeTagsRegex: '(alpha|beta|rc)'
+          sinceTag: ${{ env.gittag }}
+          releaseUrl: https://pypi.org/project/jrnl/%s/
+          verbose: false
+
+      - name: Small fixes
+        run: |
+          # Change unreleased link to correct url
+          sed -i 's!https://pypi.org/project/jrnl/HEAD/!https://github.com/jrnl-org/jrnl/!' "$FILENAME"
+
+      - name: Consistency check
+        run: |
+          if [[ $(grep '^# Changelog$' "$FILENAME") != 1 ]]; then
+            echo 'Something is wrong with the changelog.'
+            git diff -- "$FILENAME"
+            exit 1
+          fi
+
+      - name: Commit
+        run: |
+          git config user.email "jrnl.bot@gmail.com"
+          git config user.name "Jrnl Bot"
+          git add "$FILENAME"
+          git commit -m "Update changelog"
+          git push origin $BRANCH
+