v3.2.0 - Better Datetime awarness

It is now possible to provide a timezone when loading datafiles

Added

• Nilspodlib is now timezone aware!
  All loading methods for datasets, headers, and sessions now support a tz argument that is the string name of a valid
  timezone (e.g. Europe/Berlin).
  This allows access to the local start and end time in the header and a new local datetime index that can also be used
  when exporting data to pandas dataframes.

Changed

• The utc_datetime_{start/end} attributes of the header and the session are now properly reported in utc time instead
  of as naive datetime objects.
• The utc_datetime_counter is now a pandas series.