Fix method signatures, change "callback" to "callable".
Fix method signatures, change "callback" to "callable".

A callable array or a string is referred to as "callable" in PHP 5
(http://php.net/manual/en/language.oop5.typehinting.php)

sravanchandj/zend-stdlib,adamlundrigan/zend-stdlib,akrabat/zend-stdlib,weierophinney/zend-stdlib,ezimuel/zend-stdlib,MadCat34/zend-stdlib,php-refactoring/zend-array-utility