Last declaration does not require a semicolon
Skip unsupported image formats.-

 1. Skip attempting to parse images with non-png extensions

 2. Gracefully handle errors from parsing invalid png images
Some TODOs
Leave repeat|repeat-x|repeat-y alone

Images still included in sprite, however
Merge remote-tracking branch 'upstream/pr/26'
Merge remote-tracking branch 'upstream/pr/25'