- Arguments::Argument typing, such that the parser will automagically
do type conversions and print out pretty error messages if a user
tries to pass a string into an argument that should be an int, and so
on.

- Arguments::Option could provide an opposite option name for each
option, such that -quiet could have the opposite -verbose, ie, that an
Option could have a defined name for the -no-* version of the option.

