`Response` is missing methods on WASM

[bonsairobo]

So far I see these missing items:

1. Response::extensions
2. Response::version
3. impl From<http::Response> for Response

Is there a particular reason these are missing?

[seanmonstar]

Most things in WASM are added as contributors need them (I don't do any WASM development). So if they are missing, it's likely one of either:

• It hasn't been needed yet (submit a PR :))
• It doesn't have a simple way to exist in WASM.