Add a method to calculate trip distance.

[Closes #2]

Squashed commit of the following:

commit 27320b1c7ca8348f8079f999fbe957c8a6ceb27a
Author: Youssif <abdulyoussif@gmail.com>
Date:   Tue Jul 23 09:38:46 2013 -0700

    commented

commit 62c9ef0774c445d96ed7e66426a2db75ca447a6f
Author: Youssif <abdulyoussif@gmail.com>
Date:   Tue Jul 23 09:35:12 2013 -0700

    added distancew method

commit da8fc6b167fefecd9c046a971ae008da96743e0d
Author: Youssif <abdulyoussif@gmail.com>
Date:   Tue Jul 23 08:51:47 2013 -0700

    fixed division