Consider renaming `HttpConnection::version` -> `negotiated_version`

[carllerche]

This would make it clearer that the value returned is based on some sort of transport level version negotiation, whether ALPN, HTTP 1.1 upgrade, etc...

[carllerche]

My initial gut when seeing HttpConnection::version is that it would return the HTTP version in flight... via some sort of sniffing. So, if an HTTP 1.1 head is sent, the value returned from HttpConnection::version would be 1.1.

[carllerche]

cc @seanmonstar @LucioFranco

[seanmonstar]

Either is fine with me.

[LucioFranco]

@carllerche I personally perfer version with docs that explain this is the negotiated version but if it makes more sense that way then im fine with it.