Replace Travis CI with Github Actions, raise minimum version

Using Github Actions allows us to have testing on all three platforms.
Additionally, the minimum version have been raised, as versions lower
than 2.088.1 / LDC 1.17.0 do not work on Mac OSX 10.15 (Catalina)
because of the removal of a private API Druntime was using.

.github/workflows/main.yaml

@@ -0,0 +1,40 @@
+# Github action to test localrest
+#
+# Also upload the documentation to Github pages
+#
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  main:
+    name: Run
+    # Matrix configuration
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ ubuntu-18.04, macOS-10.15, windows-2019 ]
+        dc: [ ldc-master, dmd-master, ldc-latest, dmd-latest, ldc-1.17.0, dmd-2.088.1 ]
+
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 15
+
+    # The actual work being performed
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Prepare compiler
+        uses: dlang-community/setup-dlang@v1
+        with:
+          compiler: ${{ matrix.dc }}
+
+      - name: Test
+        shell: bash
+        run: dub test -b unittest-cov --compiler=${DC}
+
+      - uses: codecov/codecov-action@v1
+        with:
+          name: localrest-${{ matrix.os }}-${{ matrix.dc }}
+          flags: unittest
+          # false until we can re-trigger a single test in Github
+          fail_ci_if_error: false