Use GitHub Actions for CI

Author: wacumov

.github/workflows/UnitTests.yml

@@ -0,0 +1,24 @@
+name: UnitTests
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  test_on_macos:
+    runs-on: macos-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Build
+      run: swift build
+    - name: Test
+      run: swift test
+  test_on_linux:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Build
+      run: swift build
+    - name: Test
+      run: swift test