Merge pull request #1 from 1o1brian/master

math trick example
Updated the attendant to be more strict. Some work on the A train example.
Some work on the A train example.
Added some comments.
Comments.
Added some structure to the a train example.
added a stations dir.
Changed the exception when the attendant disapproves of the state changes made at a station.
Added goal to the readme.
New definition for attendant.
Updated the examples to follow the recommended project structure.
Removed the orig math trick.
Updated the states for the math trick example.
Rework the conductor interface and updated the math trick example.
Removed the gather_passengers method.
Readme changes to the dir structure.
Added the primary terms diagram.
Diagram update.
Updated the primary terms diagram.
Went back to orig image.