D grammar overhaul

[Trass3r]

> I hope, we agree on !in and !is, as the current lexing introduces the  
> shown parsing problems. But !is needs to be added to the IsExpression  
> rules then.

Hmm what if you have something like Templ!is(T:int)

Is http://d.puremagic.com/issues/show_bug.cgi?id=5785 fixable with grammar  
changes other that !is being one token?
I haven't had a look yet how UFCS is expressed and how it could affect  
this.