graph: rename num_transitions() as num_edges()

And in fact, rename most "trans*" as "edges*", because that what they
really are.

* src/bin/autfilt.cc, src/bin/ltlcross.cc, src/bin/randaut.cc,
src/dstarparse/dra2ba.cc, src/dstarparse/dstarparse.yy,
src/dstarparse/nra2nba.cc, src/dstarparse/nsa2tgba.cc,
src/graph/graph.hh, src/graph/ngraph.hh, src/ltlvisit/exclusive.cc,
src/parseaut/parseaut.yy, src/tests/complementation.cc,
src/tests/graph.cc, src/tests/ltl2tgba.cc, src/tests/ngraph.cc,
src/tests/twagraph.cc, src/twa/twagraph.cc, src/twa/twagraph.hh,
src/twa/twamask.hh, src/twaalgos/are_isomorphic.cc,
src/twaalgos/are_isomorphic.hh, src/twaalgos/canonicalize.cc,
src/twaalgos/cleanacc.cc, src/twaalgos/complete.cc,
src/twaalgos/compsusp.cc, src/twaalgos/cycles.cc,
src/twaalgos/degen.cc, src/twaalgos/dot.cc, src/twaalgos/dtbasat.cc,
src/twaalgos/dtgbacomp.cc, src/twaalgos/dtgbasat.cc,
src/twaalgos/dupexp.cc, src/twaalgos/emptiness.cc,
src/twaalgos/isunamb.cc, src/twaalgos/isweakscc.cc,
src/twaalgos/ltl2tgba_fm.cc, src/twaalgos/mask.hh,
src/twaalgos/minimize.cc, src/twaalgos/postproc.cc,
src/twaalgos/powerset.cc, src/twaalgos/product.cc,
src/twaalgos/randomgraph.cc, src/twaalgos/randomize.cc,
src/twaalgos/randomize.hh, src/twaalgos/relabel.cc,
src/twaalgos/remfin.cc, src/twaalgos/safety.cc, src/twaalgos/sbacc.cc,
src/twaalgos/sccfilter.cc, src/twaalgos/sepsets.cc,
src/twaalgos/simulation.cc, src/twaalgos/stutter.cc,
src/twaalgos/totgba.cc: Rename these.

src/twaalgos/postproc.cc

@@ -44,7 +44,7 @@ namespace spot
       if (a->num_sets() == 0)
 	{
 	  auto m = a->set_buchi();
-	  for (auto& t: a->transitions())
+	  for (auto& t: a->edges())
 	    t.acc = m;
 	}
       return a;