* sfz engine: implemented opcodes xfin_lokey, xfin_hikey, xfout_lokey, xfout_hikey, xf_keycurve, xfin_lovel, xfin_hivel, xfout_lovel, xfout_hivel, xf_velcurve, xfin_loccN, xfin_hiccN, xfout_loccN, xfout_hiccN, xf_cccurve