Add GDToolkit-based static checks via github actions, closes #1

.github/workflows/static_checks.yml

@@ -0,0 +1,20 @@
+name: Static checks
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+  static-checks:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: actions/setup-python@v3
+      with:
+        python-version: 3.x
+    - run: |
+        python -m pip install gdtoolkit
+        gdformat --check source/
+        gdlint source/