Use delayed delivery to get the time right.
Rename "peer" to "resource" and correlated names.

This includes an intrusive schema update.
Don't log the XMPP id attribute.
Track user data for entered chat rooms.
Add debug build rules.
Add and use convenience function Batyr_db.use_accounted.
Adjust use of options and Batyr_db.use.

  - Batyr_data: Let Node.cached_id and Muc_room.of_node return option.
  - Batyr_data, Batyr_presence: Inform about room in debug msg.
  - Move code out of Batyr_db.use where possible.
Add Cache_by_physical_bijection, adjust cache add.

  - Batyr_cache: Let cache add predictably retain the existing entry.
  - Batyr_cache.Cache_by_physical_bijection: Alternative using physical
    equality.
  - Use it for Node_cache in Batyr_data.
Add Muc_user.resource and Muc_room.cached_of_node.
Add Cache_of_hashable and rename related signatures.

Also add iteration over caches.
Use Cache_of_hashable for Muc_room node-cache.
Log the original authors of MUC messages if known.
Support ping and improve version.
Fix: Install schema updates.
Minor fix of DB update.