Add sahi support to behat
Bump Kohana to 3.3/develop branch
Refactor and update terminology on drivers
Add photoshopper driver
Provide a few useful feature definitions

Features provided:

 - Then "element" should [not] be visible
 - Given I have an image with width "" and height "" in ""
 - The "element" element should display "path"
 - The "element" element should be "" by "" pixels