Changes from MusiXTeX 126 to 127:
* introduced \meterN, \xxtuplet
* introduced \nqqb \nqqh \nqqqb \nqqqh abbreviations and
synonyms \nqql \nqqu \nqqql \nqqqu
* introduced \hap, \happ analogous to \qap, \qapp
* introduced \hbsk analogous to \hsk
* introduced \bqsk, \bhsk, \btsk analogous to \qsk, \hqsk, \tqsk
* eliminated \ds@oup