[development] Move all core modules into their own directories.

[Jeff Eaton]

> Here i think the fapi approach makes far more sense, like 
> nedjo said. Drumm's form_table element is _far_ more 
> understandable and themeable  
> than our
> current theme_table.

That approach is certainly good, and certainly cool, but it does not
replace the ability to -- when necessary -- just build a complex string
based on complex PHP logic. Template files are great for fitting
pre-rendered strings into an HTML shell, but they are terrible for
encapsulating large quantities of conditional logic.

I'd LOVE to see more template file support -- being able to throw
snippets around in small files rather than functions would be cool --
but not if it comes at the *expense* of basic function support. Perhaps
I'm misunderstanding what's really being suggested?

--Jeff