code: public JsonFluentAssert node(String newPath) {
          return new JsonFluentAssert(actual, path.copy(newPath), description, configuration);
      }
docs: Creates an assert object that only compares given node.
  The path is denoted by JSON path, for example.
  
  <code>
  assertThatJson("{\"root\":{\"test\":[1,2,3]}}").node("root.test[0]").isEqualTo("1");
  </code>
  
  @param newPath
  @return object comparing only node given by path.