Simple
case class Simple[T, B](name: Option[String], shortName: Option[Char], doc: Option[String], default: Option[B => T], reader: TokensReader[T], positional: Boolean) extends Named[T, B]
Models what is known by the router about a single argument: that it has
a name, a human-readable typeString describing what the type is
(just for logging and reading, not a replacement for a TypeTag) and
possible a function that can compute its default value