Add GitHub Actions for CI

.github/workflows/CI.yml

@@ -0,0 +1,35 @@
+name: CI
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+
+jobs:
+  test:
+    name: Test ${{ matrix.rust }}
+    strategy:
+      matrix:
+        rust:
+          - stable
+          - beta
+          - nightly
+          - 1.21.0
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v1
+
+      - name: Install Rust (${{ matrix.rust }})
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: ${{ matrix.rust }}
+          override: true
+
+      - name: Test
+        uses: actions-rs/cargo@v1
+        with:
+          command: test