v2.0.0.0

• Adds support for v204 of Sift Science's API.
• Adds support for the Workflow Status API, User Decisions API,
  and Order Decisions API.
• Version 204 of the Sift Science API is now called by default
  -- this is an incompatible change, as some fields are no
  longer returned in the v204 API (unless they are explicitly
  requested).
• Cleans up all Client methods (and the constructor) to use an
  Hash argument for optional parameters. This is an
  incompatible change.