Initial release of version 2.

Support for pydantic v2. Better naming and clearer code.

1. __env_yaml_settings_files__ -> __yaml_files__.
2. __env_yaml_settings_reload__ -> __yaml_reload__.
3. model_config can include yaml_files and yaml_reload.
4. deep_update replaces old code.
5. env variable and other sources tested.
6. Conforms with the example provided in the docs.
7. Examples are tested, docs improved.