http2 core module support

[silverwind]

http2 has different semantics for communicating the host header. In http a simple request results in these req.headers:

{
  host: 'localhost:5000'
}

while in http2 it is:

[Object: null prototype] {
  ':method': 'GET',
  ':path': '/',
  ':scheme': 'https',
  ':authority': 'localhost:5000'
}

So for minimum support, :authority could be used instead of host. It may be worth considering using :path and :scheme as well but I guess that info is probably just duplicate with req.url or req.secure.

[david-luna]

Hi,

I guess here we can follow the progressive enhancement approach. So we use http2 headers when present and fallback to the current behavior for backwards compatibility and non http2 requests.

[silverwind]

#8 does it the other way around, it first checks for host and then for :authority. Should not matter because both can probably never appear at the same time.