add & configure jshint for build task

Fixes #19 

I added [grunt-contrib-jshint](https://github.com/gruntjs/grunt-contrib-jshint) to run on the build task. After looking at the results, I turned off [newcap option](http://www.jshint.com/docs/options/#newcap) because it popped up all over the place and doesn't look like you're using that convention. The only other thing it found was a switch case that falls through that it needed to ignore.

I also added [load-grunt-tasks](https://github.com/sindresorhus/load-grunt-tasks) to autoload the grunt tasks.