Add initial GitHub CI

Author: certik

.github/workflows/ccpp.yml

@@ -0,0 +1,37 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  Linux:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: cmake
+      run: cmake .
+    - name: make
+      run: make
+    - name: test
+      run: ctest --output-on-failure
+
+  macOS:
+    runs-on: macos-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: cmake
+      run: cmake .
+    - name: make
+      run: make
+    - name: test
+      run: ctest --output-on-failure
+
+  Windows:
+    runs-on: windows-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: cmake
+      run: cmake -G "Visual Studio 16 2019" .
+    - name: make
+      run: cmake --build .
+    - name: test
+      run: ctest --output-on-failure