Trying to solve following problems of Ruby Threads:
- Don't swallow up errors, instead let them bubble up.
- Possibility to have a graceful shutdown.
More features to be implemented:
- Message passing between actors (inbox, outbox) and "piping together" two actors.
A special type of actor: one that runs an external program and writes lines to the outbox.
- Send the program's output lines as events to the outbox.
- Be able to shut down the program.
- Detect if the program exits with an error.