* Update to wit-bindgen 0.36.

The main change here is that the Rust modules now include the WIT
interface documentation as documentation comments, so that they show
up in the cargo doc documentation.

* Update CI to wit-bindgen 0.36 too.

Add the closing side of HTML comments, to fix cargo doc warnings.

* Document the now three ways to use the wasi crate.

Update the documentation to prominently describe the new wasm32-wasip2
target, to mention cargo component, and to put the existing
wasm32-wasip1 with adapter approach in context.

* Update README.md

Co-authored-by: Pat Hickey <pat@moreproductive.org>

---------

Co-authored-by: Pat Hickey <pat@moreproductive.org>

This uses `--async none` so there aren't many user-visible changes,
however one notable user-visible change is that with
bytecodealliance/wit-bindgen#1102, some functions such as `Fields::get`
have arguments that change from `&String` to `&str`.

Bump to 0.14.0+wasi-0.2.3, from 0.13.4+wasi-0.2.3, as the update to
wit-bindgen 0.37 includes some minor semver incompatibilies.

* Upgrade `wit-bindgen-rt` to version 0.39.0

* Update .github/workflows/main.yml

The only change here is #103, which doesn't significantly change any of
the bindings code.