Should import_filters behave like Rails' before_filter?

[tfausak]

I think the :only and :except options on import_filters should behave like the ones on Rails' before_filter and friends. In particular:

• You should be able to pass both :only and :except.

  import_filters Interaction,
    only: [:a, :b],
    except: [:b]
  # => Imports :a from Interaction.

• You should be able to pass a single symbol.

  import_filters Interaction,
    only: :a
  # => Imports :a from Interaction.

I changed how it behaved in a25f3c3, but I'm not sure if that was the right decision.