Added composer support

Converted to a composer package. The package can be added to a project by adding
```
    "repositories": [
        {
            "url": "https://github.com/iFixit/statsd-php-client",
            "type": "vcs",
            "reference": "master"
        }
    ],
    "require": {
            ...
            "ifixit/statsd-php-client": "dev-master"
            ...
    }
```

The class has been namespaced under` iFixit`. So 
```use iFixit\StatsD;```
is required at the beginning for the example script to work.

It would be great if you could add the package to Packagist.org
http://grossi.io/2013/creating-your-first-composer-packagist-package/