Support Machine Name Arguments

Arguments currently does a great job of allowing you to pass various types via their numeric ID's; however, it would help improve administration & URL readability if machine names were supported.

For example I have a Page which uses Panels to display taxonomy terms in a vocabulary. It has the URL Pattern: http://mysite.org/vocabulary/ Thus a typical URL looks like: http://mysite.org/vocabulary/13, but it would be much clearer if the URL could be http://mysite.org/vocabulary/program_types. Where "program_types" is the machine name of vocabulary #13.

It would also make it easier to administer, as the numeric ID is not always obvious (I never did discover how to find the numeric id for vocabularies via the front-end & had to search the DB.)