GitHub CI (#26)

* GitHub CI

* Update CI

---------

Co-authored-by: Felix "xq" Queißner <git@random-projects.net>

.buildkite/pipeline.yml

@@ -1,4 +0,0 @@
-steps:
-  - group: Build
-    steps:
-    - command: zig build

.github/workflows/build.yml

@@ -0,0 +1,19 @@
+name: Build
+on:
+  push:
+
+jobs:
+  build:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+        optimize: [Debug, ReleaseSmall, ReleaseFast, ReleaseSafe]
+    steps:
+      - uses: actions/checkout@v2
+      - uses: goto-bus-stop/setup-zig@v2.1.1
+        with:
+          version: 0.11.0
+
+      - name: Build
+        run: zig build install "-Doptimize=${{matrix.optimize}}"