sound command

Add a sound command, similar to the sound command in MSWLogo.

Description:
SOUND list
The input must be a list of pairs. Each pair specifies a non-negative floating-point frequency (in Hertz) and a non-negative integer duration (in clock ticks). The command blocks further program execution until the sound is completed. UCBLogo need not yield to other applications while the sound is being played. It does not matter what the duration of a "clock tick" is, so long as it does not vary between operating systems, versions of UCBLogo, or computers with different CPU speeds, and is much less than one second, for example, one sixtieth of a second or one millisecond.

Examples:
sound [440 200]
sound [440.0 100 493.9 100 554.4 100 587.3 100 659.3 100 740.0 100 830.6 100 880.0 100]