Enable GitHub CI

.github/workflows/format.yml

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+name: Format
+on: [push, pull_request]
+jobs:
+  all:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: hecrj/setup-rust-action@v1
+      with:
+        components: rustfmt
+    - uses: actions/checkout@master
+    - name: Check format
+      run: cargo fmt --all -- --check

.github/workflows/integration.yml

@@ -0,0 +1,16 @@
+name: Integration
+on: [push]
+jobs:
+  test:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macOS-latest]
+        rust: [stable, beta]
+    steps:
+    - uses: actions/checkout@master
+    - uses: hecrj/setup-rust-action@v1
+      with:
+        rust-version: ${{ matrix.rust }}
+    - name: Run tests
+      run: cargo test --verbose