Added pop() method to query_string, same as get(), but removes the item from the querystring
Added std::string() operator to json::rvalue (allows std::string(json["abc"]), which returns any value that isn't a container to string)
Added lo() method to json::rvalue, returns a vector of json::rvalue containing whatever a json object or list has (difference being a list has no keys)
Added keys() method to json::rvalue, returns a vector of std::string containing the keys of a json object
Made json::wvalue use either std::map or std::unordered_map instead of just std::unordered_map
Added copy constructor to json::wvalue
Added size() method to json::wvalue, returns 1 or the size of the json list.
Added constructor to create json::wvalue from std::vector
Added keys() method to query_string
Documented query_string and improved json doc
Made tests and examples for all the additions
