Test more crate permutations in GitHub CI action

Make sure we can build the crate in `no_std` mode as well.

.github/workflows/rust.yml

@@ -20,7 +20,12 @@ jobs:
 
     steps:
     - uses: actions/checkout@v3
-    - name: Build
+    - name: Build (no features)
+      run: cargo build --verbose --no-default-features
+    - name: Build (all features)
       run: cargo build --verbose --all-features
     - name: Run tests
       run: cargo test --verbose --all-features
+    # Intentionally not building docs with `--no-default-features` because some links are broken.
+    - name: Build documentation
+      run: cargo doc --verbose --all-features