onlyworlds 0.10.2

• The OKF export keeps a stub's mark. A known-of element (known_of: true, folder format §4.4) is now written with known_of: true in its concept's frontmatter, and OkfReport.known_of counts them (the command line's summary says "N known of" when there are any). Before, known_of was dropped with the other push.NOT_SENT keys, so a stub read as a whole element whose absent fields looked empty rather than unknown.