Createsend

* Created objects (clients, campaigns, lists, segments, and templates) now
retain identifiers they are given when created. This allows the following code
to be written:

python
client = Client()
client.create("Company Name", "(GMT+10:00) Canberra, Melbourne, Sydney",
"Australia")
details = client.details()


Previously, this code would have been written as follows:

python
client = Client()
client_id = client.create("Company Name",
"(GMT+10:00) Canberra, Melbourne, Sydney", "Australia")
client.client_id = client_id
details = client.details()

* Added support for including from name, from email, and reply to email in
drafts, scheduled, and sent campaigns.
* Added support for campaign text version urls.
* Added support for transferring credits to/from a client.
* Added support for getting account billing details as well as client credits.
* Made all date fields optional when getting paged results.

* Added the ability to set api_key for a CreateSend instance, rather than
only at the class level.

* Added Campaign.email_client_usage().
* Added support for ReadsEmailWith field on subscriber objects.
* Added support for retrieving unconfirmed subscribers for a list.
* Added support for suppressing email addresses.
* Added support for retrieving spam complaints for a campaign, as well as
adding SpamComplaints field to campaign summary output.
* Added VisibleInPreferenceCenter field to custom field output.
* Added support for setting preference center visibility when creating custom
fields.
* Added the ability to update a custom field name and preference visibility.
* Added documentation explaining that text_url may now be None or an empty
string when creating a campaign.

* Added support for creating campaigns from templates.
* Added support for unsuppressing an email address.
* Improved documentation and tests for getting active subscribers. Clearly
documented the data structure for multi option multi select fields.

* Added WorldviewURL field to campaign summary response.
* Added Latitude, Longitude, City, Region, CountryCode, and CountryName fields
in campaign opens and clicks responses.