deploy docs to gh-pages

.github/workflows/docs.yaml

@@ -0,0 +1,21 @@
+name: Doxygen
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  deploy:
+    name: Build and deploy documentation
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Build
+        uses: mattnotmitt/doxygen-action@v1
+
+      - name: Deploy
+        uses: peaceiris/actions-gh-pages@v3
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./docs/doxygen