Update cl-cron repository

[vindarel]

Hi,

cl-cron was developed on bitbucket: https://bitbucket.org/mackram/cl-cron (404) and it received some commits here:

https://github.com/ciel-lang/cl-cron

especially: all threads are named, use of defvar instead of defparameter, use of bt:with-lock-held instead of acquire/release, bus factor of 2 \o/

cl-cron is a nice DSL for cron-like schedulers:

(defun say-hi ()
  (print "Hi!"))

(cl-cron:make-cron-job #'say-hi)
(cl-cron:start-cron)

Thanks