code: public static RequestToken delete(String collection, String id, BaasHandler<Void> handler) {
          return delete(collection, id, RequestOptions.DEFAULT, handler);
      }
docs: Asynchronously deletes the document with {@code id} from {@code collection}
  @param collection the collection of the document
  @param id the id of the document
  @param handler a callback to be invoked with the result of the request
  @return a {@link com.baasbox.android.RequestToken} to handle the asynchronous request