starting ghost mode
add pacman style
make after fragment modifications
animated ghost
merge with master
Improve test coverage on TileSource objects
Merge pull request #38 from tangrams/iwillig/improve-tile-source-tests

Improve test coverage on TileSource objects
lint: switch away from some default arg syntax because jshint not supporting it right yet :/ (and remove some unused vars)
better cleanup when destroying GL geometry
add destroy() method for cleaning up GL textures
simplify module export syntax
added method to destroy all textures for a given GL context
added a method to destroy a GL program wrapper and free associated resources
leave in a debug line, remove a stray line
add methods to destroy a single mode instances, or all modes for a given GL context
avoid race conditions that can lead to multiple copies of render mode GL programs
more thorough clean-up on scene destroy
expose layer in demo for debugging
update build
lint