Update beam ending rules

Update beam ending rules

     - Now that beatGrouping works correctly, beam
       ending rules are not required for those values
       of beatLength which are correctly derived from
       the time signature

     - The beam ending rules for 1/16 and 1/32 notes are
       retained, however, but are extended to cover those
       moments which previously were covered by the
       deleted rules, and to cover the 2 2 time signature