Add github actions for checking code

.github/workflows/build.yml

@@ -0,0 +1,29 @@
+name: Build and check
+
+on: [push, pull_request]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        submodules: true
+    - uses: actions/cache@v2
+      with:
+        path: |
+          ~/.cargo/registry
+          ~/.cargo/git
+          target
+        key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+    - name: Build
+      run: cargo check --verbose --release
+    - name: Run tests
+      run: cargo test --verbose
+    - name: Check formatting
+      run: cargo fmt -- --check