CHANGELOG: Add recent motor updates.
## [Unreleased]
+### Added
+- Added ability to use more than one `DriveBase` in the same script.
+
+### Changed
+- Changed how `DriveBases` and `Motor` classes can be used together.
+ Previously, an individual motor could not be used when a drive base used it.
+ From now on, devices can always be used. If they were already in use by
+ something else, that other class will just be stopped (coast).
+- Changed how unexpected motor problems are handled, such as a cable being
+ unplugged while it was running. Previously, this raised a `SystemExit` no
+ matter which motor was unplugged. Now it will return an `OSError` with
+ `ENODEV`, which is consistent with trying to initialize a motor that isn't
+ there. The `Motor` class must be initialized again to use the motor again.
+- Changing settings while a motor is moving no longer raises an exception. Some
+ settings will not take effect until a new motor command is given.
+
## [3.1.0] - 2021-12-16
### Changed
