Allow center to be passed to toZXY().
Allow center to be passed to toZXY().

mapbox/tilestream,NolaMark/tilestream,frankrowe/tilestream,mapbox/tilestream,markng/tilestream,frankrowe/tilestream,zhm/tilestream,NolaMark/tilestream,zhm/tilestream,makinacorpus/tilestream,markng/tilestream,staltz/tilestream,HydroLogic/tilestream,HydroLogic/tilestream,staltz/tilestream,simonpoole/tilestream,simonpoole/tilestream,makinacorpus/tilestream