"template" for attributes

[okuramasafumi]

I came up with the API/DSL to define "templates" for attributes so that it's easier to reuse certain group of attributes with interpolation. Templates can be shared among resources and be enabled separately.

class ApplicationResource
  include Alba::Resource

  template :my_template do |*names, **options|
    # template content
  end
end

class FooResource < ApplicationResource
  use_template :my_template # Here should be some interpolation
end