Port chart.el methods to cl-generic.

Port chart.el methods to cl-generic.

cl-call-next-method cannot be used inside EIEIO's defmethod.
* lisp/emacs-lisp/chart.el: Require cl-generic at compile time.
* lisp/emacs-lisp/chart.el (initialize-instance, chart-draw):
(chart-draw-title, chart-size-in-dir, chart-draw-axis):
(chart-axis-draw, chart-translate-xpos, chart-translate-ypos):
(chart-translate-namezone, chart-draw-data, chart-add-sequence):
(chart-trim, chart-sort): Use cl-defmethod instead of defmethod.