when value properties that start with a null byte are set or retrieve…

…d (this happens when the user relies on specific Zend features) we now block such access because we do not want the user to be exposed to the peculiarities of the Zend engine

tiny changes in documentation about extension callbacks

small fix to php.ini documentation

implemented static properties as requested in issue CopernicaMarketin…

…gSoftware#58

documentation fix

fixed but in iterator

fixed empty() call

fixed example

Fixed makefile to refer to right /usr/ directory, and the operator()(…

…) methods in Php::Value are now all const (they do not modify the variable after all)