Additional changes:

• Eliminate the base subpackage and hoist all the symbols up a level.
• Switch to ts_utils.
• BaseRule: add setup method and modify Model to call it.
• RemoteWrapper: add get_topic and has_topic methods.
• Add FilteredTopicWrapper, FilteredFieldWrapper (and a few variants), and FieldWrapperList, in order to more easily handle ESS data.

Pull request: https://github.com/lsst-ts/ts_watcher/pull/37

Great addition. I would like to see a simple example/test how to use that, please see comment on github.

I the following updates and merged to develop:

• Expanded the "how to write a rule" docs, with a new section on rules that use ESS data.
• Improved the FilteredTopicWrapper docs to explain that it's probably not directly useful for rules (use FilteredFieldWrapper and its ilk, instead).
• Improved the BaseFilteredFieldWrapper docs.
• Tweaked where FilteredTopicWrapper are added to the registry: now it's done in the FilteredTopicWrapper constructor (which was already testing for existence and raising if found), rather than in Model.make_filtered_topic_wrapper. This eliminates the ability to create an unregistered filtered topic wrapper (which in turn required small change to a unit test).

I will not release a new version until I have a humidity rule, at least. There are several outstanding tickets for new rules, but humidity seems directly relevant because it makes a much better example of a rule that uses ESS data.