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.
Remove useless functools.update_wrapper call

The event descriptor object is usually not inspected and doesn't need to
be updated. Even if it were inspected, it is questionable to update its
documentation.
Update example in README