Issue 607 add modernizr

This pull request includes Modernizr for testing HTML5 features, and load them with polyfills.

This specific pull requests adds a test for window.JSON in order to support old browsers loading the minified polyfill json2 as requested by @redhog.

@redhog can you please test if it works in IE8? I've tested it locally, making the test to fail, and the json2.min.js is loaded properly.