embedURL and thubmURL are now methods on prototype object

This allows them to update the youtubeID (say a typo) and recalculate the
string with each invocation so it will reflect the change.

Updated the solution file and the instruction file to reflect the change.
updaetd starting point for challenge 2 to include new methods
Merge pull request #1 from ksolo/calculated-fields-become-methods

embedURL and thubmURL are now methods on prototype object