enable Cargo fmt check (#19)

* run cargo fmt and fix warnings.
* enable cargo fmt in GitHub Actions

Author: keepsimple1

.github/workflows/build.yml

@@ -22,6 +22,10 @@ jobs:
       run: rustup default 1.46.0
     - name: Install clippy
       run: rustup component add clippy
+    - name: Install cargo fmt
+      run: rustup component add rustfmt
+    - name: Run cargo fmt and fail if any warnings
+      run: cargo fmt -- --check
     - name: Build
       run: cargo build
     - name: Run tests