===========================
Bugs fixed
----------
* Converting between reference times now works correctly for
units with non-Gregorian calendars.
Deprecations
------------
* The boolean methods/properties on the `Unit` class have been updated
to `is_...()` methods, in line with the project's naming conventions.
========================== ======================
Deprecated property/method New method
========================== ======================
convertible() is_convertible()
dimensionless is_dimensionless()
no_unit is_no_unit()
time_reference is_time_reference()
unknown is_unknown()
========================== ======================