Spritesheet generator

This is a utility tool which creates a single spritesheet from a collection of images.
CSS is also generated, using filenames for class names.

Any file type can be dropped, but only images are processed.
Ignored files are handled with a console log, detailing the filename.

File processing includes a load progress handler. Unused here, but would be useful if running online.

Uses a 3rd party bin packing library.