Add a build system that can rewrite docstrings to reduce the huge amounts of repetition

[MaddyGuthridge]

• Figure out a way to hook into Poetry's build system to rewrite all of the docstrings
• Set up a templating system so that repetitive parts of the docstrings can be added easily

Things to template-ify:

• Note on colors using utils module
• Note on playlist track indexes

Other useful features:

• Allow for separate rewriting depending on whether we are building the documentation site, or the Python package
• Rewrite links to functions to be documentation page links (full URL for docs package, internal link for the docs site)

[MaddyGuthridge]

Working on it: https://github.com/MiguelGuthridge/transdoc