Remove JSON sourceHandler

Some weirdness happens when using this with meteor-bower. Probably
because we both registered JSON sourceHandlers. Removing the handler
means meteor will not generate fonts when the iconfont.json file
changes (unless meteor-bower is present), and a meteor restart or
an SVG change is needed to trigger the font regeneration.

Add coffeescript version constraint

Specify coffescript version

Update README.md

Regenerate when filenames change

Fix missing dependency

Only generate if necessary

Update readme to reflect cssDestBasePath

Fix version number