Refactor project structure and imports
Remove _docopt.py, the PyPi version works just as well.
Move the gui part of the settings into gui/ and refactor the way settings are accessed to make it simpler.
Merge pull request #65 from aliceh75/64-refactor-file-structure

Refactor file structure
Allow users to specifiy which mouse state arguments (eg. mouse x, mouse y) a callback should receive. Also change the KeyHandler
API to make it consistant with the MouseHandler API.
Merge branch '66-double-click-segment'