Added application/hal+json;charset=UTF-8 to the media types enum. Traverson now configures all HAL flavors to be supported by the registered HAL-specific HttpMessageConverter.
Removed nullability of media type in JsonPathLinkDiscoverer. This requires subclasses that want to support all media types to explicitly configure MediaType.ALL.
Heavily inspired by the PR submitted by @drummond but very significantly rewritten.