GitLab

This is a simplified version of @dandavison pull request (thanks dan!)

`python-nav-list-defun-positions' now uses
`python-nav-list-defun-positions-cache' buffer local variable to store
cached values of defun positions.

`python-nav-jump-to-defun' now benefits from this new cache and if
called with prefix argument it will invalidate it so new defuns are
scanned.

New Vars:
 + `python-nav-list-defun-positions-cache'