Added support for scheduling emails to the Mandrill project. Mandrill has
made this a paid feature and it will only work for accounts with a positive balance.
Fixed issues with deserializing the results from schedule-related calls.
The responses for scheduled calls are different enough from other Messages
responses to justify a separate class.
I also added tests for all scheduling functionality
Updated readme.
Merge pull request #27 from jcox92/master

Added support for scheduled emails