add CI

Author: obfusk

.github/workflows/ci.yml

@@ -0,0 +1,15 @@
+name: Haskell CI
+on: [push, pull_request]
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Setup
+      run: stack setup
+    - name: Build
+      run: stack build
+    - name: Run tests
+      run: |
+        export PATH="$(dirname "$(stack exec -- which ghc)"):$PATH"
+        make test