Pull request for #3

Resolve the following fatal error (described in #3): 

`PHP Fatal error:  Cannot access empty property in /NObjects/Object.php on line 50`

that occurs whenever a new `\NObjects\Object` is created using an associative array that contains an empty key, for example:

```
var $data = array('test' => 1212, '' => bar)
var $obj  = new \NObjects\Object($data);
// Fatal error at this point
```

This solution takes the approach of checking for and silently ignoring any values associated with an empty key. Includes tests to verify this behavior.