Class attributes are not included in mailcloak

Test a mail similar to:

```
<p><a class="btn btn-primary" href="mailto:anyone@mail.com>Contact Me</a></p>
```

before patch: no button.
After patch:
![screen shot 2014-07-24 at 19 25 24](https://cloud.githubusercontent.com/assets/869724/3691939/8efcbe4c-1357-11e4-83d9-9a2bee4dcc9e.png)