Use HTTP crate

[olanod]

The http crate is pretty much the default to use in every HTTP stack and its Request/Response types have generic body types that could be something implementing embedded_io::asynch::{Read, Write} for example. It's not no_std friendly yet but that could change(hyperium/http#563) although the PR still relies on alloc which I'm not sure if it's acceptable for this client.

[lulf]

We want to avoid alloc for sure, do you think it's feasible to change http to support that? In any case, I think #2 (using httparse) will at least remove some of the duplication we have in reqwless.

[olanod]

It doesn't look trivial to remove the dependency on alloc from http, it relies a lot on Bytes and has custom types like the HeaderMap which does allocation, it would likely be a mayor refactor that probably will introduce breaking changes.

[rmja]

I think this can be closed. The http header parsing now uses httparse.