Added support for Hubot Slack Attachments

We use the [Slack adapter](/slackhq/hubot-slack) for our Hubot, along with [Hubot Slack Attachments](/inkel/hubot-slack-attachment) (which is awesome). So this patch adds formatted responses from your hubot if you're using the [Slack adapter](/slackhq/hubot-slack) *and*  [Hubot Slack Attachments](/inkel/hubot-slack-attachment)

<sub>Note: the (bot) thing is added by Slack</sub>

![2014-12-17_17-05-24](https://cloud.githubusercontent.com/assets/1342542/5480772/225b33b0-860f-11e4-91a8-1e1487d84d04.png)