Moving to holidays name everywhere

[arkid15r]

To standardize our naming conventions, we will be removing the python- prefix from GitHub, Read the Docs URLs, and all source files for consistency. This change will not impact end users, as our PyPI package has always been named holidays. However, it may affect developers, who might need to update their git remotes accordingly. Where feasible, we will set up redirects to ensure a smooth migration experience for everyone.

If you need assistance during this process, please don't hesitate to reach out.

Thank you for using and contributing to holidays!

[arkid15r]

Alright, this is done. The repo is now under vacanza/holidays and the docs live at https://holidays.readthedocs.io/en/latest/