Update to use async queryMany.
Use dev build ov vt-query-async
added handling and tests for tiles w/o the queries layer (that exist)
Merge pull request #51 from mapbox/async-tests

added handling and tests for tiles w/o the queries layer (that exist)
Split out post-queryMany data conversion so it can be benchmarked.
Call .attributes() once per feature and store the results.
Remove distance sort -- hits are distance sorted by vt.queryMany upstream.
Switch to basic for loops for performance.
Remove unused createNulls.
Merge pull request #53 from mapbox/bench-convert

Bench convert
adjust zoom level dependent on number of tiles
Switch back to github url for node-mapnik
add threshold as argument
Add multiquery bench
better buffer checking
Merge pull request #56 from mapbox/async-better-buffer-check

better buffer checking
use faster for loops
Merge pull request #58 from mapbox/async-mapnik-update

use faster for loops
add test for lower tile threshold
typo