Proper implementation of is_callback() & is_callable(). First one only performs a check if variable type is callback, while the second checks if function exists and if can be called.

include/ph7.h

@@ -641,6 +641,7 @@ PH7_APIEXPORT int ph7_value_is_float(ph7_value *pVal);
 PH7_APIEXPORT int ph7_value_is_bool(ph7_value *pVal);
 PH7_APIEXPORT int ph7_value_is_string(ph7_value *pVal);
 PH7_APIEXPORT int ph7_value_is_callback(ph7_value *pVal);
+PH7_APIEXPORT int ph7_value_is_callable(ph7_value *pVal);
 PH7_APIEXPORT int ph7_value_is_array(ph7_value *pVal);
 PH7_APIEXPORT int ph7_value_is_object(ph7_value *pVal);
 PH7_APIEXPORT int ph7_value_is_resource(ph7_value *pVal);