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.