v2.8.2

A fix for async task event handlers, the task database plugin included,
silently stopping in a running consumer.

Improvements and fixes

• The task database plugin
  no longer holds a Redis lock around its writes. The lock expired when a write
  took longer than five seconds, and releasing it raised LockNotOwnedError.
  Since CrudDB.db_upsert is atomic (v2.8.0) the lock is not needed
  (#118).
• A task consumer stops when its async dispatcher stops running. An exception
  raised by an async handler ended the dispatcher while the consumer kept
  executing tasks, so every later event was silently dropped. The consumer now
  shuts down instead, and the application restarts
  (#118).