POpen4 provides the Rubyist a single API across platforms for executing
a command in a child process with handles on stdout, stderr, stdin streams
as well as access to the process ID and exit status. It does very little other
than to provide an easy way to use either Ara Howard’s Open4 library
or the win32-popen3 library by Park Heesob and Daniel Berger depending on your
platform and without having to code around the slight differences
in their APIs.
