Remove usage of spoon from encodeFay
Give stdout when running "ghc-pkg describe" errors

When using hsenv, I was encountering a scenario where I was only
getting "ghc-pkg describe error:".  With this added stdout, I
additionally get "ghc-pkg wrapper: Couldn't find real ghc-pkg program".
Update to haskell-src-exts-1.16.*
Bump to 0.21.0.0