Explain tasks, actions and message structure better.
Address review comment: Fix docstring.
Merge pull request #46 from hybridcluster/serialization-in-destinations-44

Serialization in destinations, not Logger.

Fixes #44.
Address review comment: mention context managers.
Merge remote-tracking branch 'refs/remotes/origin/master' into task-action-definition-18
Merge pull request #52 from hybridcluster/task-action-definition-18

Explain tasks, actions and message structure better.

Fixes #18.
Address review comment: more details on the format of timestamps.
Merge remote-tracking branch 'refs/remotes/origin/master' into no-tai64n-51
News entry for timestamp format change.