Renamed HAL-related Link and Resource to HalLink and HalResource, respectively.
Introduced Resource interface.
Removed href and rel as first-class instance variables in favor of making LinkTemplate more generic.  These are simply stored as attributes now.
Renamed HAL-related Link.java to HalLink.java.
Renamed HAL-related Resource.java to HalResource.java and now implements Resource interface from HyperExpress-Common.
Refactored LinkBuilder a bit to change the way IDs are provided: for single links, IDs are provided via the urlParam() method.  For building multiple links where a single ID changes in the URL pattern, the build(String, String…) method can be called.  Changed the attribute() method to remove the attribute if null is passed in.
Introduced HAL-specific link builder, HalLinkBuilder.