Datapoint

+ 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`.

+ Remove f-string in test

+ Bugfix for `get_observation_sites`

+ Require arguments to `get_nearest_forecast_site` and `get_nearest_observation_site`.
+ Add python 3.8 to tests and setup.py

+ Remove support for Python 3.4.

+ Fix to url case in `travis.yml` to enable releases.