This PR would subsume #3 and the work done by @Korbik

That change replaced Monad with Sync. It would also work to pass around an implicit Bracket[F, Throwable] if you want to avoid the power of Sync, although for what's going on Sync seems fine.

I'm not certain I've done the right thing with SangriaGraphQL.scala - the old IO code used IO.fromFuture but also wrapped the construction of the Future in an IO. It looks like Async.async should be safe on its own.