Add HTTP2 support for resty about resty HOT 3 CLOSED

Had a look on HTTP2 source code (https://go.googlesource.com/net/+/master/http2/). It seems Go Team has done RFC draft status for server side implementation. However Client side methods are not yet fully standardized. So I will add support of HTTP2 once Go Team release that one.

from resty.

Since Go Standard Library brought the HTTP2 usage transparently in Go v1.6 & above. In favor of that I'm closing this issue 👍. Have fun with HTTP2 & go-resty!

Excerpts from https://godoc.org/golang.org/x/net/http2
Package http2 implements the HTTP/2 protocol.

This package is low-level and intended to be used directly by very few people. Most users will use it indirectly through the automatic use by the net/http package (from Go 1.6 and later). For use in earlier Go versions see ConfigureServer. (Transport support requires Go 1.6 or later)

from resty.

Test with: Go v1.6 + go-resty
against

https://http2.golang.org/
https://http2.akamai.com/demo 

from resty.