bin: implement --output for automata

Fixes #56.

* src/bin/common_aoutput.cc, src/bin/common_aoutput.hh,
src/bin/dstar2tgba.cc: Implement it.
* src/bin/autfilt.cc, src/bin/ltl2tgba.cc, src/bin/ltldo.cc,
src/bin/randaut.cc: Fix main() to catch exceptions from the
constructor of the automaton printer as well.
* src/tgbatest/randaut.test: Add a test case.
* doc/org/oaut.org: Document it.

src/bin/autfilt.cc

@@ -515,9 +515,9 @@ main(int argc, char** argv)
   post.set_type(type);
   post.set_level(level);
 
-  hoa_processor processor(post);
   try
     {
+      hoa_processor processor(post);
       if (processor.run())
 	return 2;
     }