The Hypothesis database now supports a pub-sub interface to
efficiently listen for changes in the database, via ".add_listener"
and ".remove_listener". While all databases that ship with Hypothesis
support this interface, implementing it is not required for custom
database subclasses. Hypothesis will warn when trying to listen on a
database without support.
This feature is currently only used downstream in hypofuzz.
The canonical version of these notes (with links) is on readthedocs.