Display build status.
Lift list of supported instances to top-level.
Improve error message about unknown PTS instance.
Handle errors in command-line parsing via ErrorsT.
Improve formatting of errors without position.
Activate fomega.
Add PTS instance synonym 'fomega'.
Fix orphan instances of MonadErrors

This also moves all its instances for monad transformers together, for
extra clarity. ErrorsT instances are separate.