* src/tgbaalgos/postproc.cc: Add an option_map parameter, and use to get
extra options to pass to the degeneralization algorithm.
* src/tgbaalgos/postproc.hh: Adjust prototype, and store Boolean
variables for degeneralize() options.
* src/bin/ltl2tgba.cc: Add a -x option to fill the option map, and pass
it to the postprocessor.
* src/bin/man/ltl2tgba.x: Document the three degeneralization options.