The HTX start-line is now a struct. It will be easier to extend, if needed. Same
info can be found, of course. In addition it is now possible to set flags on
it. It will be used to set some infos about the message.
Some macros and functions have been added in proto/htx.h to help accessing
different parts of the start-line.
This file will host all functions to manipulate HTTP messages using the HTX
representation. Functions in this file will be able to be called from anywhere
and are mainly related to the HTTP semantics.