Coolify docstring for event

Okay, there are two relevant changes:

- remove the partial() stuff
- remove doctests for memory management

These are just confusing to read and a user wouldn't even get the idea
that these fail unless explicitly stated - they are not documentation
but tests.
Use function.__get__ instead of black_magic.partial

I forgot that every function is a descriptor, which makes it very
convenient to create bound member functions.