Add EMPTY tile state instead of using null for empty tiles
Add semi-transparent layer example
Replace precommit with separate check and integration-test targets
Add (incomplete) bootstrap.js externs
Add geolocation example
Merge pull request #344 from twpayne/semi-transparent-example

Add semi-transparent layer example
Merge pull request #324 from twpayne/fix-canvas-renderer-clear

Canvas renderer is not properly cleared
Merge pull request #315 from fredj/geolocation-example

Add Geolocation example
Merge pull request #312 from twpayne/speed-up-precommit

precommit target is too slow