cython-mode.el should overload python-mode's settings to recognize cdef and cpdef declarations

[ThibautVerron]

Hello,

In cython-mode, some of the mechanic is subcontracted to one of the existing python-mode's. I am not sure how all of those interact, but at least with the built-in python.el, there could be some improvement to parsing.

For example, currently, python-info-docstring-p fails to recognize that the point is in the docstring of a cdef or cpdef, which in turns means that formatting settings such as auto-filling fail.

I believe that cython-mode should provide a new value for python-nav-beginning-of-defun-regexp, for example:

(setq-local python-nav-beginning-of-defun-regexp 
	      (python-rx line-start
			 (* space)
			 (and symbol-start
			      (or "def" "class"
				  (and "async" (+ space) "def")
				  ;; new
				  (and (or "cdef" "cpdef") (+ space) (* (any word ?_))))
			      symbol-end)
			 (+ space)
			 (group symbol-name)))

It seems to do the trick for me, but I'm probably using only a subset of cython's syntax.