Add revision branch

[viable-hartman]

Adding the ability to dynamically add the Revision element so you can get additional metadata:
e.g.

Validataion Currently

{   u'AddressValidateResponse': {   u'Address': {   u'@ID': u'0',
                                                    u'Address2': u'99 SOMPLACE DR',
                                                    u'City': u'E STROUDSBURG',
                                                    u'State': u'PA',
                                                    u'Zip4': None,
                                                    u'Zip5': u'18302'}}}

Validataion with Revision Element

{   u'AddressValidateResponse': {   u'Address': {   u'@ID': u'0',
                                                    u'Address2': u'99 SOMPLACE DR',
                                                    u'CarrierRoute': u'R018',
                                                    u'CentralDeliveryPoint': u'N',
                                                    u'City': u'EAST STROUDSBURG',
                                                    u'CityAbbreviation': u'E STROUDSBURG',
                                                    u'DPVConfirmation': u'N',
                                                    u'DPVFalse': u'N',
                                                    u'DPVFootnotes': u'AAM3',
                                                    u'State': u'PA',
                                                    u'Zip4': None,
                                                    u'Zip5': u'18302'}}}

Example Usage

from usps import USPSApi, Address

usps = USPSApi('API_USER_ID', test=True)
usps.validate_address(Address(**usps_addr), with_revision=True)