Add github CI action

.github/workflows/ci.yml

@@ -0,0 +1,54 @@
+name: CI
+on: [push, pull_request]
+
+jobs:
+  build_unix:
+    runs-on: ${{ matrix.os }}
+    strategy:
+        matrix:
+          os: [ubuntu-latest, macOS-latest]
+          
+    steps:
+      - uses: actions/checkout@v1
+      - name: (macOS) Download LLVM and setup PATH
+        if: startsWith(matrix.os, 'macOS')
+        run: |
+          brew install llvm
+          echo ::add-path::/usr/local/opt/llvm/bin
+          echo ::set-env name=CPATH::`xcrun --show-sdk-path`/usr/include
+      - name: (Linux) Download LLVM
+        if: startsWith(matrix.os, 'ubuntu')
+        run: |
+          sudo apt-get install llvm
+      - name: build odin
+        run: make release
+      - name: Odin run
+        run: ./odin run examples/demo/demo.odin
+      - name: Odin check
+        run: ./odin check examples/demo/demo.odin -vet
+  build_windows:
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v1
+      - name: Install cURL
+        run: choco install curl
+      - name: Download and unpack LLVM bins
+        run: |
+          cd bin
+          curl -sL https://github.com/odin-lang/Odin/releases/download/llvm-windows/llvm-binaries.zip --output llvm-binaries.zip
+          ls
+          7z x llvm-binaries.zip > nul
+      - name: build Odin
+        run: |
+          call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Auxiliary\Build\vcvars64.bat
+          ./build_ci.bat
+      - name: Odin run
+        run: |
+          call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Auxiliary\Build\vcvars64.bat
+          odin run examples/demo/demo.odin
+      - name: Odin check
+        run: |
+          call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Auxiliary\Build\vcvars64.bat
+          odin check examples/demo/demo.odin -vet
+
+