Add beep sound

[pinterior]

Can control beep sound by:

• Setting Timer#2 counter
• Set/reset SOUND bit on port 60h.
• Read/write byte from 000cff98h.

Features not implemented:

• BCD mode
• Pause by port 46h
  • On MA20, writing non-zero RL to port 46h stops oscillation until 1(RL=1, 2) or 2 (RL=3) byte(s) are written to port 44h.
• non-50% duty cycle
  • OSDev Wiki says if counter is set to 5, actual output should be 1110011100....
• counter = 0
  • should be treated as 65536.

[captainys]

Thanks! I take it in.