Add `/.editorconfig`

## See: http://editorconfig.org/
An editor that can't handle `LF` is a sad editor indeed.  Bootstrap, Wordpress, Drupal, jQuery, Modernizr, and CakePHP all enforce `LF` line endings in their EditorConfig files.

The only editor I am aware of that can't (or couldn't last I checked) handle `LF` is Notepad on Windows.