expand score according the thru labels and expansion lists.
The thru filter is a mostly-compliant C++ implementation of the
Humdrum Toolkit thru tool (documentation). See
more information about this filter in the Humdrum Extras documentation for
thrux. Alias names of this filter can be thrux (for the nearly
100% emulation of Humdrum Extras thrux tools, or thruxx for the
same tool as this filter in humlib.