#198 - TemplateVariables now drops duplicate TemplateVariable instances.
#199 - Refactorings in HalEmbeddedBuilder.

We now provide a dedicated EmbeddedWrappers API that HalEmbeddedBuilder uses to transparently handle the collection enforcement etc. It also allow manually hand in EmbeddedWrapper instances to enforce a certain behavior independent of the global settings in HalEmbeddedBuilder.

Simplified HalResourcesSerializer in Jackson2Hal module as we now don't have to deploy custom serializers for the embedded elements anymore.

Supersedes some of the API introduced for #195.