Spawns & mansion_book spawn group

Bokkens can now be found in pawnshops & Mansion armor collections.  (They really should be more broadly distributed--sporting goods and/or milsurps--but they're also very good at this point so might throw things out of whack.)

The mansion_book spawn group has some of the rarer books as well as the MA manuals for Fencing and Niten Ichi Ryuu.  It itself is pretty low-occurrence but happens in mansion libraries, ofices, and game rooms so ought to have a pretty decent chance.