Comment that inspired this change:
<#55 (comment)>

Previously, you were unable to derive `MonadUnliftIO` using the
`newtype` strategy because `askUnliftIO` was a method of the typeclass
([related issue](#55)).

The `wrappedWithRunInIO` function is provided to help write instances
of `MonadUnliftIO` for newtypes.

In `unliftio-core` 0.2.0.0 and later, `askUnliftIO` was moved out of the
`MonadUnliftIO` typeclass. This makes `wrappedWithRunInIO` irrelevant.

This change deprecates that function, and updates the documentation to
clarify that you can now write `deriving newtype (MonadUnliftIO)`.