This is the start of an attempt to add Ptys and Ttys into
the IO:: hierarchy. It is based on an earlier Ptty distribution
by Nick Ing-Simmons.

The main differences are

 * The Ptty package has been renamed into the IO:: hierarchy and split
   into two separate packages IO::Tty and IO::Pty

 * Now uses metaconfig for configuration instead of a home-grown perl
   script. Hopefully the extra defines needed ontop of perl's config.h
   can be added into it.

The release is only a pre-release to get feedback on the configuration,
later releasees will include C library function interfaces and
exported constants.