Automatic generation of an implementation of JAX-RS-annotated interface ...

Added a way to automatically (by Java reflection) create a (dynamic proxy) implementation of a JAX-RS-annotated REST service interface.

This builds on HttpTemplate and provides an alternative way to implement calling a REST service with a bit less coding using JAX-RS annotations.

This is currently implemented just enough to support the Bitstamp's REST API: it (partially) supports @GET, @POST, @Path, @QueryParam and @FormParam. I added it to xchange-core because it is reusable. (It cannot currently be directly used with the other exchanges (VirtEx, MtGox, BTC-E) because they all require support for @PathParam.)

This adds a dependency on javax.ws.rs:jsr311-api (a 45 kB jar) to xchange-core.