Adds github actions, removes travis

Author: TheAngryByrd

.github/workflows/build.yml

@@ -0,0 +1,55 @@
+name: Build master
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macOS-latest]
+    runs-on: ${{ matrix.os }}
+
+    steps:
+    # Side by side workaround: https://github.com/actions/setup-dotnet/issues/25#issuecomment-646925506
+    - uses: actions/checkout@v2
+    - name: Use .NET Core 2.1 SDK
+      uses: actions/setup-dotnet@v1
+      with:
+        dotnet-version: '2.1.x'
+    - name: Use .NET Core 3.1 SDK
+      uses: actions/setup-dotnet@v1
+      with:
+        dotnet-version: '3.1.x'
+    - name: Use .NET Core 5.0 SDK
+      uses: actions/setup-dotnet@v1
+      with:
+        dotnet-version: '5.0.100-preview.7.20366.6'
+    - name: .NET Side-by-side
+      shell: pwsh
+      run: |
+        $version = Split-Path (Split-Path $ENV:DOTNET_ROOT -Parent) -Leaf;
+        $root = Split-Path (Split-Path $ENV:DOTNET_ROOT -Parent) -Parent;
+        $directories = Get-ChildItem $root | Where-Object { $_.Name -ne $version };
+        foreach ($dir in $directories) {
+          $from = $dir.FullName;
+          $to = "$root/$version";
+          Write-Host Copying from $from to $to;
+          Copy-Item "$from\*" $to -Recurse -Force;
+          }
+
+    - name: Build
+      if: runner.os != 'Windows'
+      run: |
+        chmod +x ./build.sh 
+        ./build.sh RunFableTests
+      env:
+        # Work around https://github.com/actions/setup-dotnet/issues/29
+        DOTNET_ROOT: ${{ runner.tool_cache }}/dncs/${{ matrix.dotnet }}/x64
+        CI: true
+    - name: Build
+      if: runner.os == 'Windows'
+      run: ./build.cmd RunFableTests
+      env:
+        # Work around https://github.com/actions/setup-dotnet/issues/29
+        DOTNET_ROOT: ${{ runner.tool_cache }}/dncs/${{ matrix.dotnet }}/x64
+        CI: true