Replib: generic programming & Unbound: generic treatment of binders

I've decided to end support for Replib and Unbound with GHC 8.8.3 and not update these libraries to GHC's latest version of Template Haskell. Since these libraries were introduced in 2006 and 2011, GHC has acquired intrinsic support for generic programming.

For future development, see the unbound-generics package, which is based on this more modern platform.