Added feature to go back an arbitrary number of pages at once.

The change makes it possible to jump back more than one step at once and is sometimes needed, e.g. in a game, when after the user finishes the game page, he gets forwarded to a "finished" page and after that should get back directly to the level select page.

Having this feature keeps the history in order and enables proper animation direction.

Use it like this:

<a href="#old" class=".back">Back</a>

in JS:

jQT.goBack('#old');

A.t.m. this only handles internal targets. Please improve where you see fit!

Kind regards,

Benjamin