missing HexString documentation

[Steven Schveighoffer]

On 2/7/18 9:59 AM, Ralph Doncaster wrote:
> It is mentioned in the literals section, but not documented:
> https://dlang.org/spec/lex.html#string_literals
> 
>  From reading forum posts I managed to figure out that HexStrings are 
> prefixed with an x.  i.e. x"deadbeef"
> 

Good catch! Even the grammar says nothing about what it is, except it 
has HexString as a possible literal.

Can you file an issue? https://issues.dlang.org

-Steve