Add Github CI workflow

.github/workflows/main.yml

+name: Testing build for push
+on: [push]
+jobs:
+  build_w32:
+    runs-on: windows-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v1
+    - name: CMake
+      run: cmake -DBONZOMATIC_64BIT="NO" -DBONZOMATIC_WINDOWS_FLAVOR:STRING="GLFW" -G "Visual Studio 16 2019" -A Win32 .
+    - name: Build
+      run: cmake --build . --config Release
+  build_w64:
+    runs-on: windows-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v1
+    - name: CMake
+      run: cmake -DBONZOMATIC_64BIT="YES" -DBONZOMATIC_WINDOWS_FLAVOR:STRING="GLFW" -G "Visual Studio 16 2019" -A x64 .
+    - name: Build
+      run: cmake --build . --config Release
+  build_linux:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Install deps
+      run: sudo apt-get update && sudo apt-get install -q -y xorg-dev libasound2-dev libfontconfig1-dev libgl1-mesa-dev libglu1-mesa-dev
+    - name: Checkout
+      uses: actions/checkout@v1
+    - name: Build
+      run: cmake . && cmake --build .
+  build_osx:
+    runs-on: macOS-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v1
+    - name: Build
+      run: cmake . && cmake --build .