system() and background procs w/ piping, redirs, ptys (Unix, Win32)

Changes for 20231003.0

• Windows now matches other platforms in that a child calling exit(N) causes result() to return N and full_result() to return N << 8. On Windows, before this change, result() was returning N >> 8, and full_result() was returning N. Programs having workarounds for this may need to condition those workarounds on $IPC::Run::VERSION.
• #157 - On Windows, avoid hang under IPCRUNDEBUG.
• Refresh "cpanfile" from Makefile.PL, to allow use on Windows.
• #163 - Normalize shebangs to /usr/bin/perl
• Fix or skip all tests recently seen to fail on Windows.
• Include t/result.t in releases.
• #168 - Make full_result() and result() Windows behavior match non-Windows.