Merge pull request #199 from naterh/get_limits

Get limits implementation
Fixed a typo in the last PR. Also added a unit test.
Fixes VirtualIP to_dict method to use vip id if available
Merge pull request #201 from vaibhavbansal/working

Fixes VirtualIP to_dict method to use vip id if available
Added mailgun module
More initial updates
Added campaign and mailbox functions
Added domain webhook functions
Lots of style cleanup.

Also moved the date formatting to utils.py, and added unit tests for it.
Removed inline comments. If explanations are needed, put them in the docstring.
Added exc handling on _create for dup domains
Removed debug info from _api_request and fixed syntax issues.
Added paste to requires
Updated exception handling for create and delete domain calls