Binary files are hard to version and collaborate around in Github, so please be gentle and checkin with @sensescape and @nvkelso before making changes.
The JSX script is run from within Illustrator to export the spritesheet image file and CSS with the texture definitions.
The YML file is the config file for the JSX script.
Output goes into the build dir.
After spritesheet generation, the PY script needs to be run to pre-blend pixels so PNG24 format images don't have dirty pixels on the transparency collar in Tangram.