Renamed .body property to the more accurate .entity.
Added ability to set body and contentType in isolation from each other.
Changed from singleton to non-singleton for Milli.
Changed 'onXXXTo methods to simply onXXX.
Added in support for registering rest apis. Closes #4.
Changed milli back to a singleton to allow registering of rest APIs in separate shared test fixtures more easily.
Renamed registerResources to registerApi to encourage registering an entire REST API in one go.