Add ol.TileCoord.createOrUpdate
Enable ol.TileCoord re-use
Re-use ol.TileCoord objects
Add ol.TileRange.createOrUpdate
Enable ol.TileRange re-use
Re-use ol.TileRange objects
Add ol.Extent.createOrUpdate
Enable ol.Extent re-use
Re-use ol.Extent objects
Eliminate an ol.TileCoord allocation
Merge pull request #519 from twpayne/tile-garbage-clean-ups

Tile garbage clean-ups