rename grunt.js to Gruntfile.js, migrate to grunt-contrib-jshint

The `grunt` command (since grunt-cli 0.4?) doesn't find "grunt.js" but does find "Gruntfile.js".  Rename the file, and migrate off of the old 0.3 Grunt `lint` task to `jshint`.

Before
![screen shot 2013-11-24 at 3 24 58 pm](https://f.cloud.github.com/assets/1527302/1609902/1de6b178-5560-11e3-9054-1d811064787e.png)

After
![screen shot 2013-11-24 at 3 28 13 pm](https://f.cloud.github.com/assets/1527302/1609903/201caf2e-5560-11e3-8b54-070c0cf8c956.png)