Items module:
* Identified flags for "owned by hostile" and "owned by trader".
* Identified an unknown uint32_t field as being the item age.
* Added and documented ClassNameCheck for more item ref types, though
they aren't used yet (other than to mark that item ref class as a
"known" class).
* Added method to get list of an item's unknown item ref classes.
* Made all unknown flags have name 'unk#', instead of some also having
the name 'u_ngrd#'.
Itemhacks plugin:
* Folded second command into "dumpitems unknown", which will list
any items which have the unknown vector field non-empty (which seems
to be associated with tasked items).
* "dumpitems unknown" will also dump any item with a set unknown flag
or with item refs of an unknown class.