Adds support for HTTP2 via axum.

[novemberkilo]

Closes #16

// @houqp

[houqp]

Thanks @novemberkilo , is the feature gate all we need to turn on this feature? I am guessing we still only need to bind to a single port and the client will negotiate with the server to use either HTTP or HTTP2?

[novemberkilo]

I am guessing we still only need to bind to a single port and the client will negotiate with the server to use either HTTP or HTTP2?

I'll check the hyper docs and also do some ad-hoc testing with curl locally. I'll report back.

[novemberkilo]

@houqp locally testing with curl is not yielding anything definitive. However, I see

And users who want HTTP/2 can opt-in, knowing they need a newer compiler version, but setting hyper = { version = "0.11", features = ["http2"] }.
Besides opting in, there wouldn't be a need to do anything else: the client and server would both be able to speak HTTP/2 automatically.

From the issue commentary for when HTTP/2 was added to hyper hyperium/hyper#304 (comment)

I've also got one of the contributors making this assertion here

[houqp]

Thanks @novemberkilo for the deepdive on this :) I filed #120 as a follow up issue.