Fix aliassing ar_attribute method
Fix aliassing ar_attribute method

The problem is that, since this is an `ActiveSupport::Concern`, the
`ClassMethods`-Module which contains the new `attribute` method is mixed in
**before** the aliassing happens. This effectively aliases the ActiveType
`attribute` to itself.

This commit attempts to fix this by renaming the overriding method
`attribute` to `at_attribute` and performing a second alias operation.

makandra/active_type