Add constant for hypertext cache pattern.

See https://tools.ietf.org/html/draft-kelly-json-hal-06#section-8.3
Merge pull request #8 from petejohanson/hypertext_cache_pattern

Add constant for hypertext cache pattern.
Initial updates for SourceRepresentations

Now - when reading a representation from a Reader you end up with a
SourceRepresentation which adds a getContent() method giving you access
to the original content that was downloaded.
Renamed to ContentRepresentation
Removed target directory from repo

Euu - how did this get in here to start with :(
Deprecated Set<> based toString methods in favor of varargs.
Removed SINGLE_ELEM_ARRAYS

Json writer will now ALWAYS expand the arrays in the content.

COALESCE_ARRAYS will now shrink _links and _embedded to a single object if included.