New matcher: `have_attributes`

see: https://github.com/rspec/rspec-expectations/issues/565

@myronmarston @JonRowe @cupakromer /cc

TODO's
- [ ] update README

![image](https://cloud.githubusercontent.com/assets/818124/3274916/b7acc98c-f335-11e3-9ff6-2a562b49c18f.png)

fixed :-)