v2.1.0

• updated and improved README
• secret_key refactored to api_key to align with docs and portal
• api_host is now known as rest_endpoint to align with docs and portal
• various doc string updates and fixes

v2.0.0

• Major refactor and simplification into generic REST client.
• API parameters are now passed as kwargs to endpoint handlers.
• Now using Requests sessions correctly.
• UserAgent is now set to track client usage and help debug issues.
• generate_telesign_headers is now static and easily extracted from the SDK if
  custom behavior/implementation is required.