add <adjustment> input and special case of <numrings>
update documentation
fix pernicious case where <x> is all zeros and <wantgain> is 1 or 2.
add input <specialoverlay>.  add another special case for <frameorder>.  add <maskimages>.  tweak the call to sound.m.
in the cases of empty <X>, we now return 1 instead of [].
add input flexibility
now occurrences of '-' are replaced with '_'
updates and new files