Setup GitHub Actions build and unit test CI jobs

.github/workflows/continuous-integration.yml

@@ -0,0 +1,37 @@
+name: Scalar
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  validate_scalar:
+    name: "CI"
+
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-16.04, ubuntu-18.04, ubuntu-20.04, windows-2019, macos-10.15]
+
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0 # Indicate full history so Nerdbank.GitVersioning works.
+
+    - name: Setup .NET Core
+      uses: actions/setup-dotnet@v1
+      with:
+        dotnet-version: 3.1.302
+
+    - name: Install Dependencies
+      run: dotnet restore
+      env:
+        DOTNET_NOLOGO: 1
+
+    - name: Build
+      run: dotnet build --configuration Release --no-restore
+
+    - name: Unit Test
+      run: dotnet test --no-restore