Log Message:
py-natsort: updated to 7.1.0

7.1.0:
Added
 - ``os_sorted``, ``os_sort_keygen``, and ``os_sort_key`` to better support
   sorting like the file browser on the current operating system - this
   closes the long-standing issue
 - Support for Python 3.9

Changed
 - MacOS unit tests run on native Python
 - Treate `None` like `NaN` internally to avoid `TypeError`
 - No longer fail tests every time a new Python version is released

Fixed
 - Various typos, missing figures, and out-of-date information in the "How \ 
it works"
 - Fix typo in CHANGELOG
 - Updated "How it works" to account for Pandas updates