0.8

• add opam lockfiles
• check channel in !tell
• config: ability to join multiple channels
• remove ISO8601, use ptime instead
• use sqlite3 for storage
  • small migrate_state tool to produce a db file from state.json
• use github actions
• remove tls_cert config option
• factoid: add max_cardinal_for_force
• add custom commands (no prefix matching at all)
• count years in !seen