URL refactoring

* When executed a block keeps its context and isn't instance
  evaled all the time
* We start with an instance_evaled block though
* no redirection on the block level, just on the method level
  e.g. when an URL does not know a shoes method it forwards
  the call to the app, as it keeps context that's cool
* for some reason this really made expert-tankpank-adjusted.rb
  fast and usable at least on my machine. Big JAY!
* meanwhile I also found out that the real performance killer
  for the menu is clear
* So much WIN in one commit. <3
removed debugging statements and cleared up the eval_block
Fix most of the specs

* give them the timer class they seem to need
* execute something in the context of an app to work
Move the if in slot.rb so we always have a current_slot
use find to get the fitting URL instead of each
specs for the context/URL
Removed debugging statements, thanks @fism88
Let the base class be extended by URLDefiner after include of URL

* this would enable us to use the following Syntax:

  class Bla
    include Shoes::URL
  end

  With this the inherited hook is just kept for backwards
  compatibility.
Merge pull request #320 from PragTob/URLRefactoring

Url refactoring