Ensure vector is adjustable & has a fill-pointer on remove-listener

[Zulu-Inuoe]

Fixes #4.
See spec documentation on delete (http://clhs.lisp.se/Body/f_rm_rm.htm)

I believe this is a better fix than #8 because it doesn't rely on the user issuing a restart, and instead just ensures we always have an adjustable array to work with, instead

[anranyicheng]

Hi, after this fixes fea2603, the result is also not correct. I fix code there:
(defun remove-listener (object event listener &key(start 0))
(let* ((silo (silo object))
(listeners (gethash event silo)))
(unless listeners
(return-from remove-listener))
(setf (gethash event silo)
(delete listener listeners
:test #'eq
:count 1
:start start
:key #'listener-function)))
(values))

(defun emit (event object &rest args)
(let* ((listeners (listeners object event))
(max-size (length listeners)))
(when (zerop max-size)
(return-from emit nil))
(dotimes (indx (length listeners))
(apply (listener-function (elt listeners indx)) args))
(do ((indx 0 (1+ indx)))
((>= indx max-size))
(when (listener-once (elt listeners indx))
(remove-listener object event (listener-function(elt listeners indx))
:start indx)
(decf max-size)
(decf indx)))
t))
then ,the result is right.