Grunt 0.4 support

I've been working on upgrading grunt-browserify to support Grunt 0.4. 

This involved renaming grunt.js to Gruntfile.js, adding grunt-contrib-nodeunit, grunt-contrib-jshint (https://github.com/gruntjs/grunt/wiki/Upgrading-from-0.3-to-0.4) and grunt-lib-legacyhelpers (https://github.com/gruntjs/grunt-lib-legacyhelpers) to the dependencies.

I also upped the version number.