Default attribute type and options in Attributor model

[konstantin-dzreev]

Attributor::Model definition tends to look heavy. It would be nice to have a default type and default options for its attributes when you define a model.
How it is:

    class Definition < Attributor::Model
      attributes do
        attribute :action, String, required: true
        attribute :project_id, String, required: true
        attribute :resource_type, String, required: true
        attribute :service, String, required: true
        attribute :service_id, String, required: true
        attribute :status, String, required: true
        attribute :task_id, String, required: true
        attribute :vendor, String, required: true
        attribute :tracking_number, String
        attribute :output, Hash
      end
    end

How it could look like:

    class Definition < Attributor::Model
      attributes(String, required:true) do
        attribute :action
        attribute :project_id
        attribute :resource_type
        attribute :service
        attribute :service_id
        attribute :status
        attribute :task_id
        attribute :vendor
        attribute :tracking_number, required: false
        attribute :output, Hash, required: false
      end
    end
end

where "String" is a default attribute type and default value for "required" is "true".