Dxrand

A demand-rate UGen which outputs random elements from a sequence. Dxrand forbid repetitions, whereas Drand allows duplicate elements to appear.

===Examples===

// sequence of constants
play {
 val in = Dxrand(Seq(3, 5, 7, 8, 11), inf)
 val tr = Impulse.kr(5)
 val v  = Demand.kr(tr, in)
 v.poll(tr)
 val f  = (v + 62).midiCps
 SinOsc.ar(f) * 0.1
}