Multiple roles available

Hey there,

This is a nice little module, I wrote a blog post about it but there is one little thing maybe you can consider.

When you select the roles you want available in the select list, you are allowed to only select one role. This means that if you select for instance authenticated users, administrators won't appear in the list. Maybe it would be a good idea to allow the selection (with checkboxes) of multiple roles. What do you think?

Cheers!
Danny