Try github actions on windows, mac and ubuntu

.github/workflows/build.yaml

@@ -0,0 +1,28 @@
+name: Checks
+
+on:
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  windows:
+    name: run on windows
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: ilammy/msvc-dev-cmd@v1.4.1
+      - name: compile
+        run: |
+          dir /s /b /o:gn
+  mac-and-ubuntu:
+    runs-on: ${{matrix.os}}
+    strategy:
+      matrix:
+        os: [macos-latest, ubuntu-latest]
+    name: ${{matrix.os}}
+    steps:
+      - uses: actions/checkout@v2
+      - name: compile
+        run: |
+          ./buildandtest