Easy Customization for Directory Local Variables

[Mauro Aranda]

I saw a post on reddit about modifying .dir-locals.el using the
Customize interface.  I didn't find anything available, so I coded
something quickly.

The code is at: https://gitlab.com/mauroaranda/cus-dir

Let me know if there could be interest in having something like this,
either in core or in GNU ELPA.  And in any case, I'll appreciate if you
have any comments about it.

(Backup your files if you're going to test it!)