Move to mkdocs and drop gastby (#151)

* update to mkdocs + add workflow

* work on mkdocs port

* update to use case list

* finalize port to mkdocs, remove old doc, keep non migrated in archive folder

.github/workflows/build-and-push.yaml

@@ -0,0 +1,16 @@
+name: Build & Push docs
+on: 
+  push:
+    branches:
+      - master
+jobs:
+    build:
+        name: Deploy docs
+        runs-on: ubuntu-latest
+        steps:
+          - name: Checkout master
+            uses: actions/checkout@v1
+          - name: Deploy docs
+            uses: mhausenblas/mkdocs-deploy-gh-pages@master
+        env:
+            GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}