PSR-0'd and the new 'txp:authors' tag.

To achieve lazy-loading affect, static method is used
since we don't have any type of controller system for
objects. This hopefully will be temporary.

This basically means that the tag code is not loaded at all
unless the tag is used in a template.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5340 2fea6a4d-a838-0410-917b-93a53c48e9d2