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

[Neil Drumm]

Dries Buytaert wrote:
> The disadvantages:
>  * PHPTemplate would become more dominant.  It's not clear how this
> can co-exist with other theme engines.

I would actually be okay with removing the whole engine system and 
simply doing PHPTemplate only. Sure theme engines are a nice feature, 
but how many are maintained and what % of themes are PHPTemplate?

-- 
Neil Drumm
http://delocalizedham.com/