hoa: swallow the neverclaim parser

This way we can easily parse a stream of HOAs intermixed with
neverclaims.

* src/hoaparse/hoaparse.yy, src/hoaparse/hoascan.ll: Add rules
for neverclaims, adjusted from src/neverparse/neverclaimparse.yy
and src/neverparse/neverclaimparse.ll.
* src/hoaparse/public.hh, NEWS: Update documentation.
* src/neverparse/: Remove this directory.
* README, configure.ac, src/Makefile.am: Adjust accordingly.
* src/tgbatest/ltl2tgba.cc, src/bin/ltlcross.cc: Use HOA
parser to read neverclaims.
* src/tgbatest/hoaparse.test, src/tgbatest/neverclaimread.test: Adjust.

configure.ac

@@ -192,7 +192,6 @@ AC_CONFIG_FILES([
   src/ltlvisit/Makefile
   src/Makefile
   src/misc/Makefile
-  src/neverparse/Makefile
   src/priv/Makefile
   src/sanity/Makefile
   src/tgbaalgos/gtec/Makefile