Tests + coverage + small fixes

* Fixes in extend() and outOfInterval()
Merge pull request #1 from AgtLucas/master

Added Grunt and minified version of countdown.js
Fixing conflicts to accept lgiraudel's pull request
Passing builds Jasmine & jshint
Improving Grunt file and readme
Slightly improving the workaround JShint global vars
Fixing strict
Fixing Jasmine test
Improving readme
Improving readme
Improving readme
Improving size
Adding a license
Adding callbacks, resolving #4
Pushing minified version
Adding jQuery events
Fixing small things
Improving the way callbacks are handled
Improving code quality
Fixing some tiny details