Add CI on Github Actions

For push and pull requests, run `swift build` and `swift test` in the
following environments:

- macOS-latest, Xcode 11.1
- macOS-latest, Xcode 11.2
- Ubuntu Xenial (Docker), Swift 5.1.1
- Ubuntu Xenial (Docker), Swift 5.1.2
- Ubuntu Bionic (Docker), Swift 5.1.1
- Ubuntu Bionic (Docker), Swift 5.1.2

Thanks, Microsoft <3

Author: dduan

.github/workflows/continuous-integration.yml

@@ -0,0 +1,51 @@
+name: Continuous Integration
+
+on: [push, pull_request]
+
+jobs:
+  macos:
+    name: macOS
+    runs-on: macOS-latest
+    strategy:
+      matrix:
+        xcode:
+          - "11.1"
+          - "11.2"
+        action:
+          - build
+          - test
+    steps:
+    - uses: actions/checkout@v1
+    - name: Xcode version
+      run: sudo xcode-select -s /Applications/Xcode_${{ matrix.xcode }}.app
+    - name: Action
+      run: swift ${{ matrix.action }}
+
+  ubuntu:
+    name: Ubuntu
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        swift:
+          - 5.1.1
+          - 5.1.2
+        ubuntu:
+          - xenial
+          - bionic
+        action:
+          - build
+          - test
+    steps:
+    - uses: actions/checkout@v1
+    - name: Action
+      run: |
+        dockerfile=$(mktemp)
+        docker=swift:${{ matrix.swift }}-${{ matrix.ubuntu }}
+        echo "FROM $docker"                    >  $dockerfile
+        echo 'ADD . FileCheck'                 >> $dockerfile
+        echo 'WORKDIR FileCheck'               >> $dockerfile
+        echo "RUN swift ${{ matrix.action }}"  >> $dockerfile
+        image=filecheck
+        docker image rm -f "$image" > /dev/null
+        docker build -t "$image" -f $dockerfile .
+        docker run --rm "$image"