* Add deep dive documentation for `tests/web.rs` of the `wasm-pack-template`
* Add docs for testing a project in addition to building
* Touch up other documentation int he deep dive and setup
* Fix a few dead links and moved pages and such
A few assorted improvements to the prerequisites documentation:
* Rust nightly/beta requirements are removed
* Wording indicating that `wasm-pack` requires `npm` has been clarified
* The dedicated Rust page was removed as it's largely just "install
Rust" nowadays
* The heading of the NPM page in the sidebar now includes `(optional)`
to clarify that it's not required.
Benedikt Werner