lbtt: take options as a string like other print functions

* src/twaalgos/lbtt.hh (print_lbtt): Take a const char* opt argument.
* src/twaalgos/lbtt.cc: Use it, select state-based
vs. transition-based using automaton property, and implement output
for generalized state-based acceptance.
* src/bin/common_aoutput.cc, src/bin/common_aoutput.hh,
src/bin/dstar2tgba.cc: Adjust usage.  We do not need to handle
--lbtt=t as a special case anymore.
* src/tests/lbttparse.test, wrap/python/spot.py,
wrap/python/tests/automata-io.ipynb, wrap/python/tests/piperead.ipynb:
Adjust.

wrap/python/spot.py

@@ -136,7 +136,7 @@ def _twa_to_str(a, format='hoa', opt=None):
         return ostr.str()
     if format == 'lbtt':
         ostr = ostringstream()
-        print_lbtt(ostr, a, bool(opt))
+        print_lbtt(ostr, a, opt)
         return ostr.str()
     raise ValueError("unknown string format: " + format)