GH #62, PR #64 - Fix IO::Pty DESTROY force-closing the slave pty. The DESTROY method (added in 1.21) explicitly closed the cached slave handle, breaking consumers like IPC::Run that hold a reference to the slave via $pty->slave() and expect it to survive master destruction. Now just deletes the internal reference and lets Perl's refcounting handle fd closure correctly.
Maintenance:
PR #61 - Simplify version variables to a single source of truth. Extract version from Tty.pm in Makefile.PL using MM->parse_version() instead of hardcoding it, use VERSION_FROM in WriteMakefile, and remove $XS_VERSION from Tty.pm.