This checks for 'TTYINV' in the environment and if found, it uses that
as a number describing a bit mask for how to show the perm_invent.
0 = current behavior, a-zA-Z in two columns (I've started referring
to those as panels because "column" is already used a lot);
1 = "show gold" => $a-zA-Z# in two columns; requires 1 more line;
2 = "sparse" => list all letters a-z in the left panel and A-Z in
the right whether there is an item in the slot or not, so that
open slots will be obvious;
3 = 1|2, "sparse" with $a-zA-Z$ instead of just letters;
4 = "in use" => full lines instead of side-by-side panels, listing
only items with non-zero obj->owornmask; currently requires 17
lines instead of 28 (or 29 for show-gold): room for top border,
15 lines of worn/wielded items, and bottom border; normal usage
would be capped at 3 weapon slots, 7 armor slots, and 4 accessory
slots, but it is possible to have more items in use (simplest
case is to pick up the iron ball while punished).
The #4 case isn't displaying its bottom border correctly and I haven't
figured out why.
If this turns out to be useful, perm_invent can become a compound or
some new option for perminv mode could be added.
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