Enable all protocols supported by upstream hyper via ALPN by default

[nagisa]

Disclaimer: I didn’t look at the code from this crate for too long.

This crate appears to be pretty much the most hands free way to get https support with hyper. However, a caveat is that this does not do any protocol negotiation and thus hyper is forced to always use http1.1.

I think it should, by default, do most of this kind of setup for the user without any additional effort on the user end.

[CryZe]

Isn't the problem that native-tls doesn't support ALPN? (Because it's only implemented on a few of the underlying native implementations).

[seanmonstar]

Correct, native-tls doesn't have ALPN support, and won't until all the backends have support added (see sfackler/rust-native-tls#113).

[RAnders00]

Do we want to reopen this given that native-tls added ALPN support now? https://github.com/sfackler/rust-native-tls/blob/master/CHANGELOG.md#v027 The documentation around the new feature seems to be rather lackluster though, the alpn flag is only mentioned in the changelog and not on the docs.rs or in the README.