Fix event firing, getDisplayed, and clickthrough on buttons

Also update earthquakes example to make use of getDisplayed
Add waitToUpdateMap option
Update borders example
Add icon attribution
Add a missing semicolon
Implement interval tree and selective removal/addition of layers

Significant performance improvement overall. The country borders demo
now runs at a decent clip, whereas before it lagged on each frame.
Update readme
Merge branch 'release/0.3.0'