Add Github Action to produce HTML manual page

.github/workflows/man.yml

@@ -0,0 +1,44 @@
+name: Manual
+
+env:
+  PROJECT: abduco
+
+on:
+  push:
+    paths:
+    - '*.1'
+
+jobs:
+  man:
+    runs-on: ubuntu-latest
+    steps:
+
+    - name: Checkout
+      uses: actions/checkout@v2
+
+    - name: Dependency
+      run: sudo apt install mandoc
+
+    - name: Manual generation
+      run: |
+        mkdir man
+        sed -e "s/VERSION/$(git describe --always)/" ${PROJECT}.1 | \
+          mandoc -W warning -T utf8 -T html -O man=%N.%S.html -O style=mandoc.css 1> \
+          "man/${PROJECT}.1.html" || true
+        wget 'https://cvsweb.bsd.lv/~checkout~/mandoc/mandoc.css?rev=1.46&content-type=text/plain' -O man/mandoc.css
+        ln -sf "${PROJECT}.1.html" man/index.html
+
+    - name: Upload
+      env:
+        DEPLOY_TOKEN: ${{ secrets.GIT_DEPLOY_TOKEN }}
+      run: |
+        git clone --depth=1 --single-branch --branch gh-pages "https://x-access-token:${DEPLOY_TOKEN}@github.com/${GITHUB_REPOSITORY}.git" /tmp/gh-pages
+        git config --global user.name "${GITHUB_ACTOR}"
+        git config --global user.email "${GITHUB_ACTOR}@users.noreply.github.com"
+        mkdir -p /tmp/gh-pages/man
+        rm -f /tmp/gh-pages/man/*
+        cp -av man/*.html /tmp/gh-pages/man/
+        cp -av man/*.css /tmp/gh-pages/man/
+        cd /tmp/gh-pages
+        git add -A && git commit --allow-empty -am "Publishing from ${GITHUB_REPOSITORY} ${GITHUB_SHA}"
+        git push origin gh-pages