Add warning for unrecognized references

this PR fix the warning on any on recognize reference due to wrong formatting or wrong place. closes #38.
@pksunkara what do you think about this:

                ss << "'" << symbol << "' formated as reference. ";
                ss << "If it is to be parsed it has to be directly after `Response` or `Request` and it's expected to be indented by 4 spaces or 1 tab";