Release 2.9.3

[andreasabel]

Release candidate:

• [x] finish testing
• [x] write release notes
• [x] upload to hackage: see https://hackage.haskell.org/package/BNFC-2.9.3/candidate
• [x] v2.9.3-rc release tag
• [x] github release
• [x] linux binary
• [x] win binary
• [x] mac package
• [x] announce on mailing list

Release BNFC-2.9.3:

• [x] finish testing
• [x] write release notes
• [x] upload to hackage
• [x] v2.9.3 release tag
• [x] github release
• [x] linux binaries
• [x] win binary
• [x] mac package
• [x] readthedocs
• [x] update bnfc webpages https://github.com/BNFC/bnfc.github.com
• [x] announce on mailing list
• [x] bump master to 2.9.4
  • [x] source/changelog
  • [x] source/BNFC.spec
  • [x] source/BNFC.cabal
  • [x] testing/bnfc-system-tests.cabal
  • [x] docs/conf.py