Adds Result Generator for API calls.

This allows for iterating over a set of results in chunks so you don't have to
transfer and then hold the entire dataset in memory.

>>> cci_iter = client['Account'].getVirtualGuests(iter=True, chunk=100, ...)
>>> for cci in cci_iter:
>>>     print cci['fqdn']

Still needs tests.
Finishes first implementation of Generator

Example usage below. This will request 10 VMs at a time from the API until 30 total starting after the first 10.
>>> for i, vm in enumerate(c['SoftLayer_Account'].getVirtualGuests(iter=True, chunk=10, limit=30, offset=10)):
>>>     print i, vm['fullyQualifiedDomainName']
Merge pull request #66 from sudorandom/generator

This adds a generator for the API binding. Resolves #65