Refactor pieces of gem structure

Most importantly, sensors are better-contained.
The overall pattern for modules is better-defined, and I've shrunken
down the main rumba.rb file to include mostly essentials.
Lots of minor formatting changes to satisfy my code OCD.
For consistency, change the main class to be "Rumba"

More robust gemspec file inclusion, dir refactoring.
Redo example code to use new changes.
Initial attempt at DSL. Untested.

Provides lots of simple commands for driving the Roomba
Experimental implementation of turn function.
Fixed math stupidity (cut me some slack, okay?)
DSL is complete! Simple commands like rotate and forwards/backwards

Soon to be expanded upon :)