rand lo hi

Generates a single random value in uniform distribution from lo to
hi.  It generates this when the SynthDef first starts playing, and
remains fixed for the duration of the synth's existence.

> do { f <- rand 200 1200
>    ; l <- rand (-1) 1
>    ; let { e = line KR 0.2 0 0.1 RemoveSynth
>          ; o = fSinOsc AR f 0 }
>      in audition (out 0 (pan2 (o * e) l 1)) }