DIP 1029---Add throw as Function Attribute---Community Review Round 1

[Dukc]

This would be a step forward, of course. But would not it be 
better to kill the one-way attribute problem in one go -meaning, 
making an antiattribute for `pure` and `@nogc` too?

In addition, I suggest that there should be a way to use 
[`pure:`/`nothrow:`/`@nogc:`/`@safe:`/their antiattributes] so 
that they only apply when attributes are not inferred - not for 
templated functions. This would also remove a big obstacle from 
front of DIP1028, as one could just mark the whole module 
`@system` with one statement without killing template `@safe` or 
`@live` inference.

Also a few smaller things:

-Why `throw` instead of `@throw`? I'm not saying it's a bad idea, 
but write the rationale in DIP.

-You mention that due to lack of an antiattribute, aggregates 
don't propagate @nothrow to their member function. Since you 
claimed "no breaking changes", I guess you meant it to be left 
that way. But the DIP should be explicit about that.