Add release workflow (#4)

Author: levonet

.github/workflows/release.yml

@@ -0,0 +1,61 @@
+---
+name: release
+
+on:
+  push:
+    branches:
+    - master
+    tags:
+    - v*.*.*
+  pull_request:
+    types:
+    - labeled
+
+jobs:
+  release:
+    if: ${{ github.event.action != 'labeled' }}
+    runs-on: ubuntu-latest
+    steps:
+
+    - uses: actions/checkout@v2
+
+    - name: Bump version on merging Pull Requests with specific labels
+      id: bumpr
+      if: ${{ !startsWith(github.ref, 'refs/tags/') }}
+      uses: haya14busa/action-bumpr@v1
+
+    - name: Update corresponding major and minor tag
+      uses: haya14busa/action-update-semver@v1
+      if: ${{ !steps.bumpr.outputs.skip }}
+      with:
+        tag: ${{ steps.bumpr.outputs.next_version }}
+
+    - name: Get tag name
+      id: tag
+      uses: haya14busa/action-cond@v1
+      with:
+        cond: ${{ startsWith(github.ref, 'refs/tags/') }}
+        if_true: ${{ github.ref }}
+        if_false: ${{ steps.bumpr.outputs.next_version }}
+
+    - name: Create release
+      uses: actions/create-release@v1
+      if: ${{ steps.tag.outputs.value != '' }}
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      with:
+        tag_name: ${{ steps.tag.outputs.value }}
+        release_name: Release ${{ steps.tag.outputs.value }}
+        body: ${{ steps.bumpr.outputs.message }}
+        draft: false
+        prerelease: false
+
+  release-check:
+    if: ${{ github.event.action == 'labeled' }}
+    runs-on: ubuntu-latest
+    steps:
+
+    - uses: actions/checkout@v2
+
+    - name: Post bumpr status comment
+      uses: haya14busa/action-bumpr@v1