* Add a first-class way of accessing caller's exports
This commit is a continuation of #1237 and updates the API of `Func` to
allow defining host functions which have easy access to a caller's
memory in particular. The new APIs look like so:
* The `Func::wrap*` family of functions was condensed into one
`Func::wrap` function.
* The ABI layer of conversions in `WasmTy` were removed
* An optional `Caller<'_>` argument can be at the front of all
host-defined functions now.
The old way the wasi bindings looked up memory has been removed and is
now replaced with the `Caller` type. The `Caller` type has a
`get_export` method on it which allows looking up a caller's export by
name, allowing you to get access to the caller's memory easily, and even
during instantiation.
* Add a temporary note
* Move some docs
* Move all examples to a top-level directory
This commit moves all API examples (Rust and C) to a top-level
`examples` directory. This is intended to make it more discoverable and
conventional as to where examples are located. Additionally all examples
are now available in both Rust and C to see how to execute the example
in the language you're familiar with. The intention is that as more
languages are supported we'd add more languages as examples here too.
Each example is also accompanied by either a `*.wat` file which is
parsed as input, or a Rust project in a `wasm` folder which is compiled
as input.
A simple driver crate was also added to `crates/misc` which executes all
the examples on CI, ensuring the C and Rust examples all execute
successfully.
