#1475 - Fix custom media type parser documentation.

Documentation for `HypermediaMappingInformation.getMediaTypes` expects to return a `List<MediaType>` which is not shown in the ref docs. Amend it with a proper parsing API as well as formatting.

src/main/asciidoc/mediatypes.adoc

@@ -858,7 +858,7 @@ public class MyMediaTypeConfiguration implements HypermediaMappingInformation {
 
   @Override
   public List<MediaType> getMediaTypes() {
-    return MediaType.parse("application/vnd-acme-media-type") <1>
+    return Collections.singletonList(MediaType.parseMediaType("application/vnd-acme-media-type")); <1>
   }
 
   @Override