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.

src/twaalgos/lbtt.hh

@@ -32,8 +32,9 @@ namespace spot
   ///
   /// \param g The automata to print.
   /// \param os Where to print.
-  /// \param sba Assume \a g is an SBA and use LBTT's state-based
-  /// acceptance format (similar to LBT's format).
+  /// \param opt if "t", force transition-based acceptance, otherwise,
+  //  default to state-based acceptance when the automaton is marked so.
   SPOT_API std::ostream&
-  print_lbtt(std::ostream& os, const const_twa_ptr& g, bool sba = false);
+  print_lbtt(std::ostream& os, const const_twa_ptr& g,
+	     const char* opt = nullptr);
 }