* spot/twaalgos/aiger.cc, spot/twaalgos/aiger.hh: Reimplement
print_aiger for speed gain, also heuristics to minimize the number
of gates as well as different encoding types have been added.
* bin/ltlsynt.cc: Make the new options for print-aiger available.
* tests/core/ltlsynt.test: Adjust tests.
* spot/twaalgos/aiger.cc: Simplify some bit operatitions. Force the
ordering of operations in aig_and, that was causing a test case to
fail on ARM, and greatly simplify the code and data structures used in
remove_unused().
* tests/core/ltlsynt.test: Adjust expected output.
To ease debugging and testing, ltlsynt can output the synthesized
strategy as an automaton, not just an aiger circuit.
Also, its exit code has been changed to something meaningful.
* bin/ltlsynt.cc: Various improvements: options, exit code, code style
* spot/twaalgos/aiger.hh, spot/twaalgos/aiger.cc,
spot/twaalgos/Makefile.am: Move the aiger printer to separate files
* tests/core/ltlsynt.test: Clean up and update test file
* tests/Makefile.am: Add the test file to the test suite
* NEWS: document the new aiger printer
* doc/org/concepts.org: document the named property "synthesis-outputs",
used by print_aiger
