New utility: 'trashman' to manage/maintain text/*.can (filter) files

Though we've had the auto-filtering feature for about a year now, with
expiration dates supported/added to every trash record, nothing was
removing the expired trash/filter items. Until now.

Check the size of your text/*.can files: if they're really big, this is
the solution.

Not yet building for Windows

Sysops will want to run this periodically (monthly?), e.g.
	trashman /sbbs/text/*.can