CI: Add a lint github workflow.

.github/workflows/lint.yml

@@ -0,0 +1,29 @@
+name: Lint
+
+on:
+  push:
+  pull_request:
+    branches: [ master ]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions-rs/toolchain@v1
+      with:
+        toolchain: stable
+
+    - uses: actions-rs/cargo@v1
+      with:
+        command: fmt
+        args: --all --check
+
+    - uses: actions-rs/cargo@v1
+      with:
+        command: clippy
+        args: --all-targets -- -D warnings