Adds Github Actions config to build compiler and run carp tests

.github/workflows/carp.yml

@@ -0,0 +1,28 @@
+name: CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-18.04
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - uses: actions/setup-haskell@v1
+
+    - uses: actions/cache@v1
+      name: Cache ~/.stack
+      with:
+        path: ~/.stack
+        key: ${{ runner.os }}-stack
+
+    - name: Build
+      run: stack build
+
+    - name: Run Carp Tests
+      run: ./run_carp_tests.sh --no_sdl