Cleanups in Affordance API and implementations of hypermedia type (de)serializers. Added a lot more domain methods and types to Link, ResourceSupport etc. to be able to move a lot of representation building logic into those.
AffordanceModelFactory is not a Spring Plugin anymore as that functionality is not needed currently as we statically look up all factories via the SpringFactoriesLoader mechanism.
Redesigned LinkRelation to become a first class abstraction in the codebase. IanaLinkRelations is now a collection of constants. Link now keeps a LinkRelation instance around instead of a plain String.
Tweaked LinkDiscoverer API to return Optional and Links instead of nullable Link and List<Link>.
Tweaked API of CurieProvider to make use of the newly introduced HalLinkRelation based on the general LinkRelation.
Additional fixes for the Kotlin extension functions. Make Kotlin build setup compile with JDK 8. Removed Objects helper class in favor of Spring's already existing Assert and it's usage in ResourceAssemblerSupport.