Updated examples to match recent Client API change.

Signed-off-by: Marek Potociar <marek.potociar@oracle.com>
Updated methods in Response that return instance of Link to clarify that all links must be resolved before returning.
Fixed JAX_RS_SPEC-347: Updated client-api javadoc.

- clarified that setting entity in a client fluent builder API overrides previously set variant-related HTTP headers. 

Signed-off-by: Marek Potociar <marek.potociar@oracle.com>