MonadSTM

Could [this MonadSTM](https://hackage.haskell.org/package/monad-stm-0.1.0.2/docs/Control-Monad-STM-Class.html) type class be adopted by the `stm` package?

It would be useful for certain abstractions such as the "console region" defined in [concurrent-output](https://hackage.haskell.org/package/concurrent-output-1.10.10/docs/System-Console-Regions.html), which currently defines its own [equivalent type class](https://hackage.haskell.org/package/concurrent-output-1.10.10/docs/System-Console-Regions.html#t:LiftRegion).

My use case involves a monad transformer atop such a thing; I want to write a type signature like:

```haskell
(MonadReader Env m, MonadSTM m) => m ()