Added many more functions to compute.c (and changed some).

Changed from threads to processes, seems easier for now.
Added a handle_sigs() function, use to create signal handlers (sigaction)

As of right now, the numbers process is the parent process, not sure if it matters. For now
I'm keeping it that way. I don't see any reason to spend time deciding which one should
be the parent. Coding will go faster if I focus on more important things.

Finally, the handle_sigs() function may need some work. I am unsure if the "void (*sa_handler)(int)"
will work for passing a function.