iosc - general purpose interpolating oscillator

iosc output[b] amplitude[bvpn] increment[bvpn] table[fvpn] sum[dpv] ;

An interpolating, table lookup oscillator.  Dynamic variables are
recommended for sum locations. Table may be either explicit, or number
may be given.  If number is n, then function floor(n) is used.

Iosc requires a much shorter table than osc for equivalent distortion
(see the Startup Kit), but runs much more slowly, of course.