Support more IO operations for ParIO monad

[sergv]

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I noticed that ParIO monad has a pretty restricted API for dealing with IO computations. Basically, it only provides a liftIO function for embedding IO actions inside ParIO. But what about IO things like bracket, mask, etc? Is there any reason why they were not added apart from a lack of working hands?

[simonmar]

By all means submit a PR. Nobody is actively working on monad-par at the moment as far as I know. The usual way to add support for bracket and co is to use monad-exception I think.