Move bounds calculation into constructor and keep track of total/curren tile.
Move bounds calculation into constructor and keep track of total/curren tile.

nyurik/tilelive.js,tomhughes/tilelive.js,paulovieira/tilelive,kyroskoh/tilelive,topwood/tilelive,mapbox/tilelive.js,gravitystorm/tilelive.js,mapbox/tilelive,Norkart/tilelive.js