[Simh] fprint_sym and parse_sym limitation

[Paul Koning]

> On Sep 22, 2015, at 7:59 PM, Mark Pizzolato - Info Comm <Mark at infocomm.com> wrote:
> 
> On Monday, September 14, 2015 at 6:20 AM, Paul Koning wrote:
>> ...
>> Ok.  This is another example of something undocumented.
> 
> True.  
> 
> Meanwhile, I was thinking this over one more time  and I realized that I had forgotten that there are already 2 user/device specific void pointers in the UNIT structure:
> 
> 	uptr->up7
> 	uptr->up8
> 
> Do with them as you wish.

Thanks.

That prompted me to look in sim_defs.h to see if there are other gems hiding.  There are.  

I'm going to make a stab at updating simh.doc with what I can see, and description of what I understand or TBS for what I see but don't know how to document.

	paul