Added an example of how to set the value of the field that a setter is being executed on.

See this question (http://stackoverflow.com/q/18049211/1157309) and answer (http://stackoverflow.com/a/19238288/1157309) on StackOverflow with an explanation of the confusion surrounding setters.
Merge pull request #82 from chill117/patch-1

Added an example of how to set the value of a field within its setter function.