Represent equivalent `enum`s the same as `bool`, make `bool` an `enum`

[CLICKME](https://github.com/glaebhoerl/rfcs/blob/make-bool-an-enum/active/0000-make-bool-an-enum.md)
Another argument for is improved documentation, since things can be attached to `bool` directly & it would get it's own doc page in the normal way.