Simplify and document .serve() options.
Simplify and document .serve() options.

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