Retinajs Versions Save

This release addresses issues caused by incorrect handling of transpiled modules.

Closes out: #273
#260
#257
#264

This release solves the problem where re-initializing retina.js would cause it to search for incorrect urls for previously processed images. It solves the problem in two ways: 1) It will no longer attempt to re-process previously processed images. 2) It gives you the option of passing in an Array, NodeList, or jQuery selection of images to the retinajs function, which will cause it to attempt to process only the elements in the collection.

Completely re-written from the ground up.

• Update to Grunt for build.
• Integrate jshint into development workflow.
• Add data-no-retina attribute to allow for exclusions.
• Configurable file name suffix. Allows users to specify a suffix of _2x as opposed to @2x.
• Minor Tweaks and bug fixes.