feat: support `cl-defun` in namespace macro

[JimMoen]

cl-defun support for #32 and kosh04/unicode-escape.el#3

[JimMoen]

after this patch:

(defalias 'names--convert-cl-defun 'names--convert-defun)
(define-namespace unicode-escape-
(defun* xxx ())
(cl-defun yyy ())
)

(fboundp 'unicode-escape-xxx)           ;=> t
(fboundp 'unicode-escape-yyy)           ;=> t
(fboundp 'yyy)                          ;=> nil

[JimMoen]

@Malabarba Plz review this PR. Thanks a lot. 🚀

[Malabarba]

Thanks for the PR!