replaceOut bufferIndex inputs

Send signal to a bus, overwrite existing signal.

> let { a = out 0 (sinOsc AR (mce [330, 331]) 0 * 0.1)
>     ; b = replaceOut 0 (sinOsc AR (mce [880, 881]) 0 * 0.1)
>     ; c = out 0 (sinOsc AR (mce [120, 121]) 0 * 0.1) }
> in audition (mrg [a, b, c])

Compare to:

> let { a = out 0 (sinOsc AR (mce [330, 331]) 0 * 0.1)
>     ; b = out 0 (sinOsc AR (mce [880, 881]) 0 * 0.1)
>     ; c = out 0 (sinOsc AR (mce [120, 121]) 0 * 0.1) }
> in audition (mrg [a, b, c])