Central Thread Pool

[Yevano]

This was going to be done, but was cancelled in part because of the hook system. The better event system described in issue #1. A central thread pool would allow new threads to be spawned arbitrarily, without needing to be managed by the programmer's code. For now, all threads would have to end for the program to terminate. This could possibly be changed in a runtime setting, but I doubt its necessity. Example:

--@import me.threads.MyThread

function MyProgram.main()
    for i = 1, 8 do
        MyThread.new(i):start()
    end
end

[Yevano]

Merged into master as of commit 50.