pxmake 0.16.0

New features

• When creating px object from data frame the ordering in cells1 is determined
  based on the type in the data frame.

Breaking changes

• Require R version >= 4.1. (#376)
• Store all non-figures variables in data table as character instead of as
  factors. (#375)

Bug fixes and minor improvements

• Make tests an examples 'fail gracefully' if URL can't be reached, to comply
  with CRAN policies. (#379)