Making extension fully browser-agnostic

Also added some doc too
Extension related changes

We changed extension.js in a way that changes had to be made here too.

Hoping for that not happening anymore.
Chrome adaptations

Now, chrome.js implements an proxy to xhr calls.

Please, refer to in-file comments to a more verbose, friendly and
detailed explanation.
Merge branch 'feature-PHPShell-event-listeners' into develop

Resolves #9
Linebreak harmony

;)
Shared event handler shouldn't be inside prototype

Since each instance should have it's very own event handler, there is
no reason to maintain an event handler on prototype. It is, from now
on, a static property.
Getting rid of PHPShell.setup method

This has became useless since token catch is not an setup
responsibility anymore.
Sync'ing extension interface

We don't need bypass setup() call anymore.

Some other cool things sync'd.
Fixing static setup listener