Added "grunt build" task to created minified version

@jehna @ionutvmi

Addresses issue https://github.com/VerbalExpressions/JSVerbalExpressions/issues/5 "Minified Version is missing"

###  Changes

Added "grunt-contrib-uglify" to package.json "devDependencies"
Created "grunt build" task that runs qunit, then creates VerbalExpressions.min.js in a gitignored _dist_ folder.
Updated MIT license URL to http://opensource.org/licenses/MIT
Updated Readme.md with instructions on how to build the minified version