Replace core language HexStrings with library entity

[Nick Treleaven via Digitalmars-d]

On 17/03/2015 03:28, Andrei Alexandrescu wrote:
> On a higher level: there's no subset of the language that's at the same
> time sufficiently complex and sufficiently obscure to make its removal a
> net positive.

q"" delimited strings. No one uses them (used once in all of Phobos). 
They are obscure and add some complexity to lexing D.