We should deprecate C-style declarations

[Ellery Newcomer]

Don wrote:
> Before TDPL is published, I think we should finally get rid of C-style
> declarations. Supporting two styles of declarations just causes
> confusion, and AFAIK it doesn't have any benefits -- for example, it
> doesn't significantly help in porting code from C. D declarations are
> just better. And there are bugs such as this one, which seem to require
> abandoning C declarations:
> 
> bug #2392 Parsing ambiguity between function pointer declaration and
> function call
> 
> At the very least, can we make sure that TDPL doesn't commit us to
> retaining them forever?
> 
Yes please please please please please