Including a module after a call to attributes doesn't work

[louismrose]

As described in the example "should work when include is last" of specialisation_spec.rb, including a module after calling attributes results in unexpected behaviour:

module Author
    extend Attributable
    attributes articles: []
end

class Columnist
  extend Attributable
  attributes :column
  include Author
end

Columnist.new(articles: [:teen_advice])
# => KeyError: Unknown attributes: articles

When the include occurs before the call to attributes, the error disappears.

[louismrose]

One approach that might fix both this issue and issue #2 could be to add the accessors, equality, etc. methods when the attributable class is initialized to create a new object, and not when the call to attributes is made.