Producing state-based acceptance is now part of the postprocessing
routines.  That means we can more easily simplify automata with
state-based acceptance (using autfilt -S --small --high, for instance)
and as as side-effect, ltl2tgba can produce GBA.  However the result of
ltl2tgba -S is often larger than that of ltl2tgba -B.

* src/twaalgos/postproc.cc, src/twaalgos/postproc.hh: Implement
the SBAcc option.
* src/bin/common_post.cc, src/bin/common_post.hh: Implement -S.
* src/bin/autfilt.cc, src/bin/dstar2tgba.cc, src/bin/ltl2tgba.cc,
src/bin/ltl2tgta.cc, src/bin/ltldo.cc: Adjust.
* src/tests/sim3.test: Augment test case.
* NEWS, doc/org/ltl2tgba.org, doc/org/autfilt.org: Document it -S.