Fixed error if second parameter in Attrio::Types::Integer.typecast - nil...

Fixed this case:
````ruby
class MyUser
  include Attrio

  define_attributes :as => :settings do
    attr :skill_ids, Array, :split=>',', :element => { :type => Integer }
  end

  def initialize()

  end

end
````

````
2.0.0p247 :002 > u = MyUser.new
 => #<MyUser skill_ids: nil> 
2.0.0p247 :003 > u.skill_ids = '1,2,3'
NoMethodError: undefined method `[]' for nil:NilClass
        from .../www/attrio/vendor/gems/attrio/lib/attrio/types/integer.rb:7:in `typecast'
        from .../www/attrio/vendor/gems/attrio/lib/attrio/types/array.rb:16:in `block in typecast'
        from .../www/attrio/vendor/gems/attrio/lib/attrio/types/array.rb:14:in `map!'
        from .../www/attrio/vendor/gems/attrio/lib/attrio/types/array.rb:14:in `typecast'
        from .../www/attrio/vendor/gems/attrio/lib/attrio/builders/writer_builder.rb:28:in `block in define_typecasting_method'
        from (irb):3
        from .../.rvm/rubies/ruby-2.0.0-p247/bin/irb:16:in `<main>'

````

and second variant not implemented: 

````ruby
module Attrio
  module Types
    class Array < Base
 
  #...
      def self.element_options(element)
        element[:options] || {} # this line
      rescue
        {}
      end
    end
  end
end
````

sorry, without tests