Add Grunt.

It will:
 - lint the code
 - test the parser
 - concatenate files
 - minify JS

For now it is configured to run tests and lint JS.

The maintainable Gruntfile approach is used.

Read more at: http://www.thomasboyt.com/2013/09/01/maintainable-grunt.html
Merge pull request #4 from hkdobrev/grunt

Add Grunt.