Add wasm-opt optimization build step (#29)

* Optimize wasm with Binaryen wasm-opt

* Friendly message and pretty colours

* Print optimized size compared to original

* Fmt

* Update src/cmd/build.rs

Co-Authored-By: Hero Bird <robin.freyler@gmail.com>

* Update src/cmd/build.rs

Co-Authored-By: Hero Bird <robin.freyler@gmail.com>

Co-authored-by: Hero Bird <robbepop@web.de>