Fixed an issue with OptiPNG 0.7 or higher

Check the return code from OptiPNG instead of STDERR since OptiPNG outputs all activity logs into STDERR by default.
allow whitespace and other non-image attributes before the URL
Display activity logs from OptiPNG 0.7 or higher

Monitor updates on STDERR and redirect to logger.
Option to cache everything to a JSON file and then exit (I assume this would be done as a pre-deploy step)
Don't kill process, just use callback
Funny business. More logging for throwing error upon missing option.
Too many callbacks for CSS.
Don't freak out if we can't find an image.
Don't throw any errors if something fails to upload, just keep chugging along.
Merge pull request #24 from nozaq/patch-optipng0.7

PNG optimizations fail with OptiPNG v0.7 or higher
Merge pull request #29 from JoshuaGross/master

Fix CSS parsing: non-image attributes and whitespace
added update