Merge pull request #1 from Khouba/master

Exception for no images
Rewritten task function, removed old grunt 0.3-compatible code, better options handling, better error handling. Corrected doc example syntax.
Increased version to 0.1.2.
Added padding option.
Added '-strip' command-line parametr in imagemagick convert command to remove sRGB profile tags that can cause color mismatch in Firefox.
Added evenPixels option to force dimensions of sprites to be multiple of 2.
Merge branch 'master' of https://github.com/karfcz/grunt-sprite-packer
Added support for bunch of options: background,	format, quality and evenPixels.
Fixed typos in readme
Added 'timestamp' variable description to readme.