* Refactor the `types.rs` types and structures
A few changes applied along the way:
* Documentation added to most methods and types.
* Limits are now stored with the maximum as optional rather than a
sentinel u32 value for `None`.
* The `Name` type was removed in favor of just using a bare `String`.
* The `Extern` prefix in the varaints of `ExternType` has been removed
since it was redundant.
* Accessors of `ExternType` variants no longer panic, and unwrapping
versions were added with "unwrap" in the name.
* Fields and methods named `r#type` were renamed to `ty` to avoid
requiring a raw identifier to use them.
* Remove `fail-fast: false`
This was left around since the development of GitHub Actions for
wasmtime, but they're no longer needed!
* Fix compilation of the test-programs code
* Fix compilation of wasmtime-py package
* Run rustfmt
