Provides the functions to parse the response provided by the Overpass API.
parse({:ok, {:xml, String.t}}) :: {:ok, %Overpex.Response{nodes: term, relations: term, ways: term}}
parse({:ok, {:json, String.t}}) :: {:ok, %Overpex.Response{nodes: term, relations: term, ways: term}}
parse({:error, String.t}) :: {:error, String.t}