[Phoenix] Refined Phoenix Specification

[Andreas Wuest]

Hi

In order to be able to create a sophisticated roadmap, I have refined 
the Phoenix specification quite a bit.

I have reworked some of the "general/special features" into use cases, 
showed how the project is going to be decomposed, and finally added the 
features relating to the use cases.

Comments on the specification are definitely welcome.

-- 
Kind regards,
Andi