* The new exceptions Duplicate_parameter, Mismatched_bracket, and
  Unrecognized_flag were created, though Mismatched_bracket has only the
  beginnings of an implementation.
* [--] is implicit in function definitions, and a single -- terminates the
  search for flag options, setting $-- in the process.
* There are some documentation updates that are unrelated to the current
  changes, as well as documentation of them, and some documentation of option
  handling thus far.