#128 - Severe refactoring regarding LinkDiscoverers.

The LinkDiscoverer interface is now a Plugin<MediaType> to allow selecting a discoverer per media type. We also provide a LinkDiscoverers wrapper around a PluginRegistry for easier injection.

Dropped DefaultLinkDiscoverer as the above mentioned changed prohibits the usage of a discoverer without a media type. Clients that previously used DefaultLinkDiscoverer should switch to JsonPathLinkDiscoverer with a custom JsonPath expression and media type.

@EnableHypermediaSupport now supports multiple HypermediaType values set to be able to set up support for multiple hypermedia formats. Admittedly, the only currently supported type is HAL but we prepare for the addition of other (e.g. Collection/JSON or the like). We changed the infrastructure setup taken care of by @EnableHypermediaSupport to not enrich all ObjectMapper instances with our HAL modules but explicitly register an ObjectMapper with the application context and then registering a custom MappingJackson(2)HttpMessageConverter with the HandlerAdapter instances present in the ApplicationContext. We skip the registration if an already registered MJ2HMC has an ObjectMapper already supporting the Spring HATEOAS mixins.

Removed some compiler warnings.

src/main/java/org/springframework/hateoas/LinkDiscoverer.java

@@ -18,12 +18,15 @@ package org.springframework.hateoas;
 import java.io.InputStream;
 import java.util.List;
 
+import org.springframework.http.MediaType;
+import org.springframework.plugin.core.Plugin;
+
 /**
  * Interface to allow discovering links by relation type from some source.
  * 
  * @author Oliver Gierke
  */
-public interface LinkDiscoverer {
+public interface LinkDiscoverer extends Plugin<MediaType> {
 
 	/**
 	 * Finds a single link with the given relation type in the given {@link String} representation.