New matcher: `have_attributes`

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

see: https://github.com/yelled3/rspec-expectations/commit/046f4d8b2be076c521532c6ed0884ad2c78c0920