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.