Switch to use promises where possible
test/utils.js -> test/test_helpers.js
Try to fix import issues
Move helper method out of common module
Add back extra spaces
Always resolve in the buildTile method
track tile loading/error state
worker broker: support promise rejections
minor cleanup on selection map
sync tile state to main thread when tile fails to load
update build
remove stray debug
Merge pull request #60 from tangrams/promise-instead-of-callbacks

Switch to use promises where possible