Replace core language HexStrings with library entity

[Biotronic via Digitalmars-d]

On Monday, 16 March 2015 at 12:53:24 UTC, Nick Treleaven wrote:
> 0b1010 binary literals (even though C++11 supports them)
> 0xABCD hex literals (but useful for porting C)

And while we're at it, why not remove those pesky base-10
literals as well? Shouldn't be too hard to write dec!"123456"
instead of 123456. :p