Consolidate reference documentation

The documentation under the reference heading is generally more out of date and less detailed than what we have in the inline docs on docs.rs. For the documentation that covers a specific higher level concept, like the rules of hooks, we should move it into the essentials or guides section. For documentation that covers a specific hook like `use_coroutine` we should remove the page and point people to the docs.rs reference instead

We could also embed the docs.rs documentation into a subdomain on our docsite like [web-sys](https://rustwasm.github.io/wasm-bindgen/api/web_sys/) does. Our search indexing should be compatible with any html file so we could make the docs.rs reference pages show up in the guide search results as needed