Add HTTP/2 parser

[kirillv]

Currently http-parser is used to parse responses and requests. But it has no support of http/2 only 1.1. It would be great is Filtering engine would be able to proccess 2 version of http protocol.
Thanks in advance.

[TechnikEmpire]

😨 Oh dear. Is HTTP 1.1 getting deprecated any time soon? That's probably the only thing that would make me jump to supporting this with any sense of priority. You are right though, it should be a goal to eventually support it, but given that it's a brand new shiny protocol I think we're more than safe for a decade to simply advertise as HTTP/1.1