Implement forgotten settings for case preserving

[nox]

Turns out I didn't implement the server-side public setters for #2480, oopsie.

[zonyitoo]

What's the differences between http1_title_case_headers and http1_preserve_header_case?

[nox]

http1_title_case_headers: Sec-WebSocket-Key becomes Sec-Websocket-Key.
http1_preserve_header_case: Sec-WebSocket-Key is sent as is.

Note that you can combine the two, so that existing headers in a given request will preserve their original case, but headers added by Hyper itself (say, date) will use the title case.

[zonyitoo]

So http1_title_case_headers won't make date become Date?

[nox]

It will, but http1_preserve_header_case won't on its own, that's why you need the two. Preserve means there was an original casing to begin with (i.e. the casing that was found when on the wire when parsing the HTTP message), that's not the case for headers emitted by Hyper itself.

[nox]

Also, note that Hyper still doesn't let you pass arbitrary header case, as HeaderCaseMap is still private, so http1_preserve_header_case is only useful for proxies right now, where you receive a request from one end, and send it with the client on the other end.

[nox]

This now includes @zonyitoo's fix from #2510.

[seanmonstar]

Thanks for the quick fix!