add a "worker broker", in charge of sending messages from main thread to a worker
each message sent to the broker has a 'type', and the broker invokes a method of that name on the worker
any return value from the worker method is then sent back to the main thread, and provided to a callback
this allows a typical async JS callback pattern to be used when invoking worker functions
Merge branch 'master' into worker_broker
lint, docs, minor API modifications
Merge branch 'master' into worker_broker
Merge branch 'master' into worker_broker
remove dead code
small changes to worker broker API, and add docs
continue converting worker calls to use broker pattern
worker should add error to tile object
add support for async responses to worker broker, via promises
if a worker method returns a promise, the broker will wait for it to resolve before calling back to the main thread
fix nasty bug causing tiles to jump between workers (when worker id 0 would eval to null)
use spread operator to allow worker log passthrough to send multiple arguments
switch tile build process to use worker broker callback pattern
update build
Merge branch 'master' into worker_broker
lint
Tile class work
Test some interactions between the Scene object and the Tile object
Pass the TileSource to the Tile object
Move over zoom calculation to tile source