Support JSON Pointer in @HttpExchange interface

Sometimes we need extract data from child node instead of root document.
For example get index mappings from ElasticSearch:

@HttpExchange("http://localhost:9200")
public interface ElasticSearchIndexOperations {

	@GetExchange("/{index}/_mapping")
	@JsonPointer("/${index}/mappings")
	Mappings getMapping(@PathVariable String index);

 }

NOTE: placeholders in @JsonPointer("/${index}/mappings") need to be resolved base on method parameters.

Start by tracing the @HttpExchange interface response handling and the proposed @JsonPointer annotation. Check how method parameters such as @PathVariable are resolved, then define completion as extracting the requested child node and resolving ${index} from method parameters, as shown in the Elasticsearch example.