Proposed improvements to the separate compilation model

[Dicebot]

I really like this and never never understood reason behind 
automatically generated .di files, as much as difficulties with 
separation of interface and implementation. If there is one thing 
that prevents me to say that D module system is 100% better than 
C++ - here it is. If there is something I would like to write by 
hand in first place, it is .di file for sure, because it is the 
one intended to be read by broader programmer count.

Add in my proposals about protection attributes and inner linkage 
and that would have been module system I really love.

But I tend to agree that importance of this issues is not urgent 
enough to prioritize it anyhow. Adding "prepproved" enhancement 
request after convincing D community may be enough for now.

Regarding CTFE - it is a reason to not use this layout for 
generic algorithm libraries and similar stuff, but there is no 
point in allowing application module code for CTFE by an accident.