Add clippy to CI

In order to keep the codebase linting cleanly add a CI job to run
clippy.

.github/workflows/rust.yml

@@ -73,3 +73,19 @@ jobs:
         env:
           DO_WASM: true
         run: ./contrib/test.sh
+
+  Clippy:
+    name: Clippy
+    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 clippy
+      - uses: actions-rs/cargo@v1
+        with:
+          command: clippy
+          args: --features=rand-std,recovery,lowmemory,global-context --all-targets -- -D warnings