create model for clients going from representation to ALPS

[mamund]

• client consumes a representation (e.g. HTML, Cj, Atom, etc.).
• client finds ALPS reference (header, media type, body)
• client parses response into internal ALPS representation <!>

need a general way to instruct client developers to be able to leverage the ALPS information consistently for each media type representation. this is the opposite of servers - they will use ALPS information to generate a media type representation.