Add support for Subscription Statements List/Retrieve

[apparelmagic-heath]

The current SDK does not offer a way to list subscription statements
(https://developers.maxio.com/legacy/http/api-endpoints/legacy-statements/list-subscription-statements)
or read a subscription statement
(https://developers.maxio.com/legacy/http/api-endpoints/legacy-statements/read-statement)
as a PDF.

If there is a non-legacy API/SDK equivalent that I may have missed which allows this, please let me know!