New options and features

Thanks for the great work! I've been looking for something like this as I try to transition into Ubuntu from OSX! :)

Here a few fixes/improvements I made to the project:
* Add margins, usable screen area, and padding options.
* Renamed width,height to columns,rows to lessen confusion of new options.
* Ensure box selecting is limited to being > 0 and < width,height, respectively.
* Bind 'Escape' as a hotkey to hide a visible ration dialog.
* Add feature to auto-hide ration dialog after arranging windows, similar to Divvy. Currently defaulting to True.
* Improve CONFIG parsing code.