suport merge method for Phalcon\Config

general code was:
``` if typeof instance !== "object" ``` -> ``` if !(instance instanceof self) ``` and
``` if typeof value === "object" && typeof instance->{key} === "object"``` had the same situation, but in the iteration Zephir throws some exception like
``` Phalcon\self does not exist ```, please pay attention to this case, thanx

Also config can have numerical keys as properties (example ``` PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8' ```), why do u exclude numerical type?