Website directory structure

[Gervase Markham]

At the moment, with the exception of /releases and /security, which I 
did at 2.16-time, the website has most things dumped in the root 
directory. I'd like to fix this, and make e.g. a /developer one for the 
Developers' Guide/Localisers' Guide etc., and maybe another one or two 
as well.

If anyone particularly cares how this is done, let me know - otherwise 
I'll just do what seems sensible.

Gerv