0.17.0: sites, one OpenSite record per page

The sites collection (PR #82): one OpenSite record per page (logicsrc.com/opensite), read by written-down rules with robots.txt and /.well-known/opensite.json honoured; /c/sites// shows the record and the card as X, Slack, iMessage, Discord, LinkedIn and WhatsApp would draw it; /c/sites/add reads any address now; /api/v1/sites by GET and POST. Twelve house sites walked from their sitemaps. 0.16.0 was IGDB (#81); this is the version of its own (#83).