Sort scopes are passed the order (asc/desc) directly

Derek, I was hoping you could take a look at this. I'm thinking for simplicity sake, sort scopes need only be passed the order ('asc' or 'desc') rather than a hash that also contains the attribute name. Was there some use case you wanted to have the attribute available?

I'm talking about this:
```ruby
class User < ActiveRecord::Base
  scope sort_status, -> criteria { order("confirmed_at #{criteria[:order]}") }
  # vs..
  scope sort_status, -> o { order("confirmed_at #{o}") }
end
```