This attribute was used to attach the right docstring node to the right Attribute object. Now it uses AST node navigation (with the .parent attribute) instead for fetching the docstring node for an ast.Assign.

This change might not be worth it, on the one hand it removes a attribute beeing mutated at different palces in the code, but replaces this kind of "unsafe" state tracking (meaning not with pop() and push()) by some more verbose solution that involves adding the .parent attribute on all nodes.

The zopeinferface extension needed to be adjusted as well because it relied on the docstring assigment feature in an implicit way, now it's explicit what we're doing.

…docstring assignments or irgnore it.

…/pydoctor into experimental-refactor-astbuilder