Allow "caps" for stats

[dfabulich]

Sometimes you want stats to range between arbitrary numbers, e.g. 1-5. It would be nice to have a way to automatically cap a stat, so if I add 3 points to a stat capped at five, it just remains at 5.

[dfabulich]

Subroutines (via gosub) might be another good(?) way to handle this. Note that in many cases you don't really want a silent cap, but rather you want to do something unusual when you hit the cap, e.g. if wounds > 5, you die.