Added Gruntfile

Setup the Gruntfile to create a minimised version of the javascript
file.
Updated Gruntfile

Added less compilation.
Fixed the banner so it didn't have an extra comment close.
Removed direct CSS dependency

This gives the user of the library more options in how they want to
manage bringing in the CSS for the editor.
Moved source files into src directory.
Removing dependency on Require.js

CommonMark.Editor now load itself into the global scope if it cannot
load itself as an AMD module.
Updated the demo

In an effort make the demo smaller updated it so that it no longer uses
require.