Add the ability to query status for a PR

Example:

`hubot status jekyll/jekyll 2001` will give you back

```
https://github.com/jekyll/jekyll/pull/2001 - error - The Travis CI build could not complete due to an error
```
Fix up the message sent back with the status
Merge pull request #4 from jekyll/ci-status

Add the ability to query status for a PR