All source code files as well as README.md, .gitignore, and various configuration files have been updated with an SPDX license identifier, changing license from CC0-1.0 to MIT. The copyright year has been updated to 2023, and the copyright holder's email address has been corrected from 'winni@neessen.dev' to 'wn@neessen.dev'. An MIT license text file has been additionally added.
