Make some monsters steal food and possibly other items. [$40]

Need several pieces of infrastructure for this:
Monster flag for STEAL_FOOD.
Adjustment to monster::plan() to make monsters with this flag consider food a target.
Probably a new monster function take_item() for the monster to use on it's target once it acquires it, which will probably flip the monster plan to either being neutral or running away.
Code in monster::die() to dump contents of inventory when monster is killed.

Similar flag/code for STEAL_SHINY, possibly others.
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