Adds runner file to allow easier testing in IRB.
Adds methods for showing total passenger count on train, and letting the train know whether it's full.
Refactoring methods.
Refactors tests.
Renames exit_train method to release_train and adjusts tests.
Adds carriage class. Carriages can accept and release passengers and know when they are full.
Minor updates to comments.
Minor update to comments.
Minor tweaks.
Updates runner with Person class.
Adds passenger class and tests.