def of_type(*types)
      Specification.new(reader, result.dup{ |r| r.with_types = types.flatten })
    end
def of_type(*types)
      Specification.new(reader, result.dup{ |r| r.with_types = types.flatten })
    end
Limits the query to certain event type(s).
 {http://railseventstore.org/docs/read/ Find out more}.

 @types [Class, Array(Class)] types of event to look for.
 @return [Specification]