Further refactored the QL parser.
Further refactored the QL parser.

drolbr/Overpass-API,mmd-osm/Overpass-API,drolbr/Overpass-API,drolbr/Overpass-API,mmd-osm/Overpass-API,drolbr/Overpass-API,drolbr/Overpass-API,mmd-osm/Overpass-API,mmd-osm/Overpass-API,drolbr/Overpass-API