Add github actions

.github/workflows/fmt.yml

@@ -0,0 +1,20 @@
+on: [push, pull_request]
+
+name: rustfmt
+
+jobs:
+  fmt:
+    name: Rustfmt
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - run: rustup component add rustfmt
+      - uses: actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --all -- --check --config merge_imports=true