Add workflow to publish documentation

Closes #35

.github/workflows/publish-docs.yml

@@ -0,0 +1,58 @@
+name: Push Documentation
+
+on:
+  push:
+    branches:
+      - master
+  workflow_dispatch: 
+
+
+jobs:
+  push-documentation:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v2
+
+      - name: Install Doxygen Portable
+        run: |
+          sudo apt-get update
+          sudo apt-get install doxygen
+          sudo apt-get install graphviz
+          doxygen --version
+          
+      - name: Generate documentation
+        run: |
+          doxygen doxygen.config
+
+      - name: Set config settings
+        run: |
+          git config --global user.email "noreply@action.bot"
+          git config --global user.name "GitHub Action Bot"
+          git config --global push.default matching
+
+      - name: Clone gh-pages branch
+        run: |
+          mkdir gh-pages
+          git clone --quiet --branch=gh-pages https://${{ secrets.USERNAME }}:${{ secrets.PAT }}@github.com/baynezy/SiteWarmer.git ./gh-pages
+          cd gh-pages
+          git status
+
+      - name: Clean gh-pages folder
+        run: |
+          cd gh-pages
+          find . -type f -not -name '.git*' -delete
+          git status
+
+      - name: Copy contents of documentation folder into gh-pages folder
+        run: |
+          cp -r ../documentation/html/* .
+          git status
+
+      - name: Commit and push changes
+        run: |
+          git add --all
+          git status
+          git diff-index --quiet HEAD || git commit -m "skip ci - static site regeneration"
+          git status
+          git push --quiet