Entity#attributes should only include declared attributes #13

class MyEntity
  include Minimapper::Entity

  attribute :my_attrib
  attr_accessor :my_accessor
end

e = MyEntity.new(my_attrib: 1, my_accessor: 2)
e.attributes # => { my_attrib: 1, my_accessor: 2 }

e = MyEntity.new(my_attrib: 1, my_accessor: 2)
e.attributes # => { my_attrib: 1 }