Mouse click

I am going to need mouse click functionality for CRM corpus responses. I have not yet done all the event handling gobbledigook, but this at least provides the ability to poll the mouse button status. @Eric89GXL and @drammock, please take a look and comment when it's convenient.
WDYT about translating the numbers to 'left', 'middle', 'right' for the user? It makes for more readable code like `if 'left' in ec.buttons:`.