Addedd support for h2c requests (HTTP/2 without TLS)

[mzdeb]

Hi,

It's my first PR here, and first in golang. ;) Thank you very much for your hard work on this project.

Probably support for h2c might be done better, so any suggestions welcome.

[tsenart]

How does this relate to golang/go#14141?

[mzdeb]

As bradfitz wrote:

I've already accepted a ton of logic for h2c. My policy has been and remains: it should be possible for people to do h2c via a separate package, but it won't be supported by default.
All the pieces should be there now for you to glue it together yourself.
For server-side support you'll need to hijack in the PRI * HTTP/2.0 Handler and then call http2.Server.ServerConn.

So currently H2C is quite simple for client to implement. When golang/go#16581 will be resolved, all options from http.Transport will be also available.

[awinder]

I've gotta 👍 this issue because I'm currently impacted by the same issue and it looks like several months have elapsed without any closure from the upstream golang PRs. Any chance of reviving this?

[tsenart]

LGTM