Log Message:
Update to happy-1.19.12

1.19.12
* Fix for building with GHC 8.8.x
* Move custom Setup preprocessing steps into a separate executable,
  like Alex

1.19.11
* Fix for building with GHC 8.6.x

1.19.10
* Fix polymorphic (rank-n) non-terminals
* Fix for GHC 8.8.1

1.19.9
* Fix cabal warnings
* Bump upper bounds
* Fix build with GHC 8.4.1-alpha

1.19.8
* Fix issue #94 (some grammars don't compile due to new type
  signatures introduced to allow overloading to be used)

1.19.7
* Fix misisng test suite files in the sdist

1.19.6
* Manually generate Parser.hs using Makefile before sdist, to fix
  bootstrapping problems with cabal sandboxes & new-build
* Documentation fixes
* Fixed GLR support
* new option -p/--pretty prints the grammar rules (only) to a file
* Added generation of additional type signatures to enable use of
  typeclasses in monadic parsers.