The problem with legacy Nitrogen codebase

The main problem which leads to code growing in wf_core is an assumption that
XHR calls would be made to the same URL as a page, i.e. each page has its own
XHR binding endpoints same as a page endpoint. Due to that page state was
introduced:

first_request -> that blows the initial page
postback_request -> that talks over XHR

and for unknown reason static_file state. I removed all this stuff and
redirected all postbacks to single endpoint let's say /websockets. Anyway in
postback we have all pickled information needed to call Module:event(Args).
From the other side websocket handler nature is that you should do all
operation inside callbacks, its not like you do just websocket:send() from
erlang.

So this refactoring not only means to purify codebase but also opens a way to
implement any transport under nitrogen. Thats why websocket port of nitrogen
comes so easy and later XHR fallback with Bullet implemented in couple minutes.
Doing that within previous wf_core codebase would be impossible. And doing this
in cowboy and bullet callbacks makes N2O aware of any transports.