Transpose note down by top note of arpeggio

[pinobatch]

Some composers like to stuff three-part harmony onto a single channel using arpeggio, with the top voice carrying the melody. Transposing a note down by the top note of the arpeggio would make the melody easier to follow when reading a score. I propose to enable this by adding - before the arpeggio.

absolute
# this
EN-47 g'4. EN-38 c'' EN-59 e''2.
# does the same as this
EN47 c'4. EN38 e' EN59 g'2.