Ephemereal duck types

v3.2.0 (2018-11-30)

Major changes

• Removed dependency to PyEphem. This package was the "Python2-compatible" library to deal with the xephem system library. Now it's obsolete, so you don't need this dual-dependency handling, because ephem is compatible with Python 2 & Python 3 (#296).
• Raise an exception when trying to use unsupported date/datetime types. Workalendar now only supports stdlib date & datetime (sub)types. See the basic documentation for more details (#294).