new Exception => new \Exception

Autoloading this library via Composer results in an Exception each time the Codebird library attempts to throw an Exception:

```
[30-Apr-2013 13:22:07 America/New_York] PHP Fatal error:  Class 'Codebird\Exception' not found in /Users/[...]/api/vendor/mynetx/codebird-php/src/codebird.php on line 453
```

This merge request would solve that issue.