API : changed tool_tip -> tooltip

As it should be one word
API : tweaked api on FileHandler
API : changed how extension filters are handled
API : made ToolBase objects callable

This is to play-nice with ipython parallel (because bound instance
methods are not pickable).
ENH : over-ride default pickling methods to force init to be called
ENH : added class method `id` to `BaseDataHandler`
BUG/API : fixed kwarg handling for csv kwargs

 - now need to pass csv kwargs as a dict, does not automatically collect
   kwargs to pass through (can see ways to re-implement this if needed)
 - fixed bug where unpickling was not unnesting kwargs properly