Update the code

[MatthewDaws]

Trying to run the tests on a recent (mid 2021) install of Python reveals a huge number of errors, not limited to

• Changes in the geopandas API, especially around CRS setting
• Warnings about escaping in docstrings
• Use of np.float
• Failure of logging tests, probably due to changes in Python logging API
• Abuse of pytest fixtures

There is almost no chance I will have time or motivation to fix these...