get & set support private & protected property now.

Sometimes we do need to access private or protected object properties (such as write your own serializer). But the old get & set didn't support this feature. for example:

```C++
void getPrivate(Php::Parameters &params) {
    Php::out << params[0].get(std::string("\0Test\0hello", 11)) << std::endl;
}
void setPrivate(Php::Parameters &params) {
    params[0].set(std::string("\0Test\0hello", 11), "World");
}
```

```PHP
<?php
    class Test {
        private $hello = "hi";
    }
    $t = new Test();
    getPrivate($t);
    setPrivate($t);
    var_dump($t);
?>
```

Expected output is:
```
hi
object(Test)#1 (1) {
  ["hello":"Test":private]=>
  string(5) "World"
}
```

The actual output is:
```

PHP Fatal error:  Cannot access property started with '\0' in /home/andot/git/valuector/test.php on line 7
```

This patch fixed it.