BPF-AMBDEF
Arguments: bpf-obj &optional scale-[[length]] [generic-function]
Defines an ambitus for the chords using a bpf editor. Two chords should be drawn, one for the lower and one for the upper limits of the ambitus. This box should be connected to the 'ambitus' entry of a solver.
'bpf-obj' receives the ouput of a BPF box. 'scale-length', if given,
'bpf-obj' receives the ouput of a BPF box. 'scale-length', if given,
should be an integer specifying the number of chords.
