Initial Parsedown structure in JS

It is suited for both Node.js and non-Node.js environment.

Structure inspired by underscore.js
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