module to instantiate Moose objects using a single argument

 MooseX::SingleArg allows Moose instances to be constructed with a single
 argument. Your class or role must use this module and then use the single_arg
 method to declare which attribute will be assigned the single argument value.
 .
 If the class is constructed using the typical argument list name/value pairs,
 or with a hashref, then things work as is usual. But, if the arguments are a
 single non-hashref value then that argument will be assigned to whatever
 attribute you have declared.