Add memory cache for tileset loading.
Add memory cache for tileset loading.

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