[wp-docs] plugins that load their own themes

[Kaf Oseo]

It would help if we didn't use phrase "theme plugins".

The reason for some doing so possibly lies with Ryan's announcement
that when a theme has a functions.php it will be loaded after the
plugins. And though the idea is to offer some plugin-like access to
the API hooks and whatnot, the term 'plugins' used for this is just
going to confuse people.

They're theme-specific functions. Let's call them that.

-Kaf