[CM] Snd 13.6

[Bill Schottstaedt]

Snd 13.6

added environment-ref|set!
      char-position and string-position (moved from Snd to s7)
      make-formant-bank and formant-bank? (and changed formant-bank again)
      comb-bank, all-pass-bank, and filtered-comb-bank generators
      one-pole-all-pass generator moved to C
      envelope-interp, rxyk!cos, and rxyk!sin moved to C
      yet another version of oscil-bank

removed mus-file-prescaler and mus-prescaler  -- these no longer serve any purpose.

checked: gtk 3.7.14, 3.8.0|1, sbcl 1.1.6.

Thanks!: Michael Edwards, Mike Scholz