v4.0.0

• #46 Add
  -p, --prefix to label every output line with its command and
  -l, --label <name> to name a command, with colored labels like
  docker compose.
• #22 Stop the
  commands behind npm run too: on Unix each command runs in its own process
  group and parallelshell stops the whole group.
• #28 Run commands
  without exec, so export, cd and a && b work.
• Stop background processes a command left behind and wait for every stopped
  process before exiting. Ctrl+Z and fg pause and resume commands. Commands
  are stopped even if parallelshell itself is killed.
• Breaking: a failing command, --timeout and closed output now stop the
  others with SIGTERM instead of SIGINT. Commands can't read from the terminal
  anymore (use askpass or credential helpers for passwords).