Add CI workflow

We start our continous integration with running all tests there.

Author: cmeissner

.github/workflows/main.yml

@@ -0,0 +1,24 @@
+name: CI
+
+on:
+- push
+- pull_request
+
+jobs:
+  tests:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python
+      uses: actions/setup-python@v2
+      with:
+        python-version: '3.x'
+    - name: Prepare test environment
+      run: |
+        python -m pip install --upgrade pip
+        make test-setup
+    - name: Run all tests
+      run:
+        make test-all