[development] Splitting hook_menu into hook_menu and hook_router

[Vladimir Zlatanov]

> While I'm not opposed to the idea, I still fail to see the big win.   
> Just because it provides logical separation or do you have a better  
> reason?  
Well... That is a reason enough in it's own right. Currently the menu
hook has two concerns, menu placement and routing. While the init could
benefit from one place - it is simpler. The logic of what happens later
becomes too complicated leading to those annoying bugs/features like
Access Denied for custom links in menu, etc...

It is simpler, at least has the potential to be simpler, in my book taht
is better. Extra api? if the two apis are easier to understand than the
current one I think it is better.