#131 - Add Traverson hypermedia client API.

Introduce Traverson as means to traverse hypermedia based APIs by providing a set of relation names to discover and follow to access the final representation. Traverson allows to specify a parameter map that will be used  to potentially expand the URIs discovered.

We currently support LinkDiscoverer based relation discovery, which means that relations in HAL representations can be found by simply stating their names. Alternatively JSON path expressions can be used (starting with a $).