Fixes CSS generation for PNGs larger than IE8 data URI limit.

Fixes #75
Adds an example PNG who's data URI length is over IE8's data URI limit.

References #75
Make sure to put the png file in the svg css, in case an svg doesn't exist
Remove unnecessary comment
Example just png folders
Should address #79
Merge branch 'master' of https://github.com/filamentgroup/grunticon
Fix #78, grunticon shouldn't run if there are no files in the source directory
Adding travis hook
Fix for travis
Update README.md

Adding travis build status.
Updating pngcrush-installer
Merge branch 'master' of https://github.com/filamentgroup/grunticon
Update README.md

Changelog updates.
Another fix for #78, including in 0.6.8 push right away
Merge branch 'master' of https://github.com/filamentgroup/grunticon