cargo fmt/clippy all the things + make them mandatory in CI

.travis.yml

@@ -6,3 +6,8 @@ matrix:
   fast_finish: true
 before_install:
   - sudo apt-get install -y libasound2-dev libdbus-1-dev
+script:
+  - cargo update
+  - rustup component add clippy rustfmt
+  - cargo clippy --all-targets -- -D warnings
+  - cargo fmt --all -- --check