Add trip_duration method.
Add power source method
Merge remote-tracking branch 'origin/master' into calculate-trip-time

Conflicts:
	train.rb
Fixiing bug
Merge pull request #1 from KaoruDev/calculate-trip-time

Calculate trip time
Squashed commit of the following:

commit 891e8ad26542d0d5510e1504546f0497a50e512d
Author: Kaoru <dev@kaoruk.com>
Date:   Fri Sep 20 10:36:04 2013 -0500

    Fixed calculations and add a method to return a distance based on duration
defined a method