Uniting library traits

[Eduard Staniloiu]

Cheers everyone!

I have a question that popped in to my head due to the fact that 
we have `traits` written into both druntime and Phobos.

In druntime, we have the `core.internal.traits` module, which has 
quite a few traits copied form Phobos' `std.traits`.

Would it be a bad idea to move `std.traits` and probably 
`std.meta` into druntime?

What is the rationale (preferably with pros and cons) of keeping 
them split across libraries?

In my humble opinion, I think those should reside in druntime as 
then they would be accessible to a larger chunk of library code.

Kind regards,
Edi