Specifically a way to reload the plugin and switch vterms. This is
important in case the plugin is borked and stops accepting keyboard, the
user can switch to a vterm, fix the plugin and reload it to get things
working again without running into data loss.

This monad allows keybindings to look and feel like one is writing
blocking code with constructs like:

key <- nextKey
when (key == x) $ do
  key2 <- nextKey
  ...
...

but this code does not block or do any io shenanigans, it under the hood
just changes the handler on the state. It seems pretty awesome and opens
the doors for some pretty expressive key bindings.

Turns out that the one on Github is ancient and the project was moved
long ago ... which is quite annoying that. No wonder where all the
confusion was coming from.