Moose role that extends class' constructor to accept single arguments

 MooseX::OneArgNew lets your constructor take a single argument, which will be
 translated into the value for a one-entry hashref. It is a parameterized
 role with two parameters:
  * type - The Moose type that the single argument must be for the one-arg form
    to work. This should be an existing type, and may be either a string type or
    a MooseX::Type.
  * init_arg - This is the string that will be used as the key for the hashref
    constructed from the one-arg call to new.