Release v2.1.0-pre.1

This release is a major architectural change to use the Home Assistant Data Update Coordinator. There are no new features or fixes in this release, so you can cleanly downgrade to the most recent v2.0.x release if needed.

Home Assistant provides a DataUpdateCoordinator class to help manage fetching data for entities as efficiently as possible with a single periodical poll, then letting entities know as soon as new data is available for them.

Please report problems in issue #67.