Squashed commit of the following:

commit 5f95bec0f379ee338d4c06b44b1bc67e83149fe0
Author: MakerSquare Student <students@themakersquare.com>
Date:   Fri Dec 6 11:51:47 2013 -0600

    Add comments to trip distance.

commit 361b83bbf13e91e848d58c1357daddb18db5b631
Author: MakerSquare Student <students@themakersquare.com>
Date:   Fri Dec 6 11:43:38 2013 -0600

    Add trip_distance

	[Closes #2]
Add a method to calculate trip distance.