starting ghost mode
add pacman style
make after fragment modifications
animated ghost
merge with master
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
mark scene when destroyed to prevent errors on further calls
leaflet layer: unhook leaflet events and destroy tangram scene when layer is removed
merged with master
ghost sprite demo
added animated sprite strip support
pull geometry forward in depth range to avoid far clipping plane