missing HexString documentation

[Adam D. Ruppe]

On Wednesday, 7 February 2018 at 17:36:56 UTC, Seb wrote:
> Octal predates GitHub, hexString is new:

Yes, I know, I was there :)

Heck, in the hexString forum thread, I argued that people knowing 
this pattern is really useful because then they can do all kinds 
of custom literals like stripping hexdumps.

Back in the octal days, I was thinking we should replace several 
literals with the new pattern and do more user-defined stuff. 
Notice who is cited in this old article 
http://www.drdobbs.com/tools/user-defined-literals-in-the-d-programmi/229401068


But, in the years since, I've changed my mind... somewhat. The 
pattern is still good and it being customizable is awesome, but 
it is a minor hassle and even that minor hassle has hurt the use 
in practice, like in the druntime examples.

We can do user defined literals for base X if we need more. But 
since octal is used by operating system apis and that'd under 
phobos... the phobos solution isn't great. Hex strings I think 
are going to be basically the same in time. The library artifact 
will sit there, unused.