The properties defined in a base class after the subclassing are missing from the subclasses.

``` ruby
require 'disposable'

class A < Disposable::Twin
  class Sub < self
  end

  property :foo
end

A::Sub.definitions
# => {}

class B < Disposable::Twin
  property :foo

  class Sub < self
  end
end

B::Sub.definitions
# => { "foo" => #<Disposable::Twin::Definition> }
```
