Replace Travis with Github Actions

Because Travis is putting large restrictions on their open-source offer,
we have to move away from it.

Author: Geod24

.github/workflows/ci.yml

@@ -0,0 +1,27 @@
+name: CI
+
+on: [ push, pull_request ]
+
+jobs:
+  build:
+    name: Run
+    strategy:
+      matrix:
+        os: [ ubuntu-latest, macos-latest, windows-latest ]
+        dc: [ dmd-latest, ldc-latest, dmd-2.085.1, ldc-1.14.0 ]
+
+    runs-on: ${{ matrix.os }}
+
+    steps:
+    - uses: actions/checkout@v2
+    - uses: dlang-community/setup-dlang@v1
+
+    - name: 'Build & Test'
+      shell: bash
+      run: |
+        dub test --compiler=$DC -b unittest-cov
+
+    - name: Upload coverage to Codecov
+      uses: codecov/codecov-action@v1
+      with:
+        flags: unittests