This commit leverages two new attributes in the Rust compiler,
`#[wasm_custom_section]` and `#[wasm_import_module]`. These two attributes allow
removing a lot of hacks found in wasm-bindgen and also allows removing the
requirement of `wasm-opt` to remove the unused data sections.
This does require two new nightly features but we already required the
`proc_macro` nightly feature and these will hopefully be stabilized before that
feature!
Right now Webpack probably has the most mature support for loading wasm modules,
so let's show off how to do that! Additionally this commits hello world as an
example to the repository.
