Datapoint

+ Remove python 3.8 support
+ Update GitHub location in docs

+ Fix bug in API request when twice-daily forecast was used.

+ Use one timestep per day for daily forecasts.
+ Add twice-daily forecast option to split daily forecasts into day and night.
+ No longer strip 'day', 'night', 'midday', 'midnight' from element names in daily and twice-daily forecasts.

+ Correct elements to camelCase for daily forecasts.
+ Add option to convert numeric significant weather code to string description

+ Modernise packaging and build tooling and infrastructure.
+ Migrate to use new MetOffice DataHub. This required many changes, for more
details see the 'migration' page of the documentation.

+ Update versioneer
+ Add pythons 3.9, 3.10, 3.11, 3.12 to tests and setup.py.
+ Remove support for python < 3.8
+ Remove deprecated `new_old` and `future_old` functions.
+ Add `__str__` functions to `Timestep`, `Element`, `Day`, `Site`
+ Add element to `Forecast` to track if forecast is daily or 3 hourly
+ Change `id` variable in `Forecast`, `Observation`, `Site` to `location_id`.
+ Change `id` variable in `Element` to `field_code`.