Renamed 'peel' to 'suspend' and 'restore' to 'resume'.

While updating the documentation I realised that 'suspend' is probably a better name for 'peel' than 'peel', and if I call it 'suspend' I can then call 'peel' 'resume', which communicates nicely that 'resume' does the opposite of 'suspend'.

This also means that the 'restore' name no longer clashes with the `mask $ \restore ->` idiom.

Updating the documentation after this change was very painful, but I think the result is probably clearer now than what came before. I hope.
Pretty much completed the documentation for Control.Monad.Lift.

Unless I fuck everything up again.