Add a GitHub build/test action

...

Author: helje5

.github/workflows/swift.yml

@@ -0,0 +1,21 @@
+name: Swift
+
+on:
+  push:
+    branches: [ develop ]
+  pull_request:
+    branches: [ develop ]
+  schedule:
+  - cron: "0 9 * * 1"
+
+jobs:
+  build:
+
+    runs-on: macos-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Build
+      run: swift build -v
+    - name: Run tests
+      run: swift test -v