Forcing a note to a particular staff line

Occasionally, it is necessary to move a note's pitch to a certain staff line or space, with no regard to the clef (e.g. to indicate percussion on a non-percussive instrument.) The built-in Pitch_squash_engraver does just that. This snippet provides two Scheme shortcut functions, \squashTo and \middleLine. Don't forget to include the correct engraver in the Voice context.