Create builder for versioned APIs

[bbarker]

Different versions of the Docker API support different functions or variations of functions. Currently there are two Format.scala files defining the JSON inputs and outputs of the REST API, but this would be rather painful to maintain for many versions. While we don't need to support everything up front, a builder for a version-specific API would be ideal, so that a user only needs to specify their version at run time to get the right set of functions.

This could possibly be done with:

• macros?
• lazy evaluation of methods to specific function values, etc.