Add support for multiple arguments

```
/**
 * Module dependencies.
 */

var Log = require('../lib/log')
  , log = new Log('notice');

log.emergency('a emergency %s', 'message', {a:'b'});
```

should output:

```
[Tue, 06 Sep 2011 03:21:10 GMT] EMERGENCY a emergency  message { a: 'b' }
```

as `console.log` does.
