Courier v0.3.1

Quick update to the v0.3 release fixing some issues with the initial version.

Fixes

• Fixed the generated Responder impl to actually generate MessagePack responses when the
  msgpack feature is enabled, and to not generate JSON responses when the json feature is
  disabled. (#1)
• Fixed the generated Responder impl to check the Accept header to determine what format
  to use for the response body. (#1)

Courier v0.3

Initial release supporting v0.3.x of Rocket. Provides support for deriving FromData and Responder for any types that implement serde::Deserialize and serde::Serialize, respectively. Also supports using both JSON and MessagePack formats for data transfer.