Use clearer names for three methods of spot::scc_info
scc_info::used_acc() and spot::info::used_acc_of() have been renamed to scc_info::marks() and scc_info::marks_of(). scc_info::acc() has been renamed to (the already existing and redundant) scc_info::acc_sets_of(). Old names have been deprecated. * spot/twaalgos/sccinfo.hh, spot/twaalgos/sccinfo.cc: implement it. * spot/twaalgos/dtwasat.cc, spot/twaalgos/isweakscc.cc, spot/twaalgos/remfin.cc, spot/twaalgos/sccfilter.cc: update names. * NEWS: documentate it.