Dev event monad

[turion]

Spinoff from #171 where I thought I'd need a monad that allows event broadcasting. Turns out I don't actually need it.

[jmatsushita]

I'm giving this a spin in a terminal-noschedule branch and I think you might need to add the following in the flake.nix:

(...)
      name = "rhine";
      packageNames = [ "rhine-gloss" "rhine-terminal" "rhine-examples" ];

      hpPreOverrides = { pkgs }: new: old:
        with pkgs.haskell.lib; with haskell-flake-utils.lib;
        {
          monad-schedule = old.callHackageDirect { pkg = "monad-schedule"; ver = "0.1.2.0"; sha256 = "sha256-7zXI37brdrqlgiRo/RseP0iMhBferzDM+Qiu5F1hhus="; } {};
        };
(...)

And in the stack.yaml files:

- monad-schedule-0.1.2.0@sha256:640b0dc483c2c0fef3fbbe91ddd2685aa13621fc1457497659d6c4c4d2d1ee74,1803