Get output of a background application
Problem to Solve If a program run by the VM in the background from the REPL outputs anything, we want to capture it and make it available via a command. Otherwise, it will be printed to the user's REPL session, which could be very annoying.
Further Details Right now, the only opcode that prints anything is PRTS. It prints to stdout. Printing to stdout when not running in the background and printing to a buffer when running in the background will most likely be needed. Not sure on implementation yet.