Squashed commit of the following:

commit 7ad7522fed4d060441ba29cc27fc639a6aec59e1
Author: Qualquer Valor <qualquervalor@gmail.com>
Date:   Fri Dec 6 15:40:45 2013 -0600

    fixed trip_distance method logic

commit 07098d096e15870d96e9ac2f9e0facc7c99aa4c6
Author: Tyler Wasden <twasden@gmail.com>
Date:   Fri Dec 6 15:33:05 2013 -0600

    Add documention for trip duration method, time in hours speed in mph

commit f1032925d78dd232712212044498470fb04f9ce2
Author: Tyler Wasden <twasden@gmail.com>
Date:   Fri Dec 6 15:25:36 2013 -0600

    Add method for trip duration in train.rb