tt550 TODO (Ken,  N7IPB):
	Support for multiple VFO's and Memories.  The TT550 doesn't
	really have VFO's or Memories since it's strictly a software
	controlled radio, but they can easily be simulated in software.
	I already support a split mode since the TX and RX control is
	separate.  Adding support for VFO-A, VFO-B and memory channels 
	will be done next.

	The optional encoder with keypad is supported for changing frequency
	only, along with F1 changing the stepsize.  The other function keys
	have no current assignments.  I can add hard-coded Function keys as
	I did with F1 but maybe a more generic solution can be determined.

	In addition the keypad is not supported.  Hamlib has no apparent way
	to make use of the numeric keys.  We probably need to add a callback
	for key data.

	IF-Shift:  IF-Shift code is in place but I see no way in hamlib to make 
	use of it.  The Icom dual pass-band tuning is supported,  but not just
	simple IF shift.  Or maybe I just missed something.

	TX Audio Monitor Volume - no hamlib support - RIG_LEVEL_TX_MON?
	CW Sidetone Volume - no hamlib support - RIG_LEVEL_SIDETONE?
	Transmit Audio Source and Volume select - no hamlib support - RIG_LEVEL_LINEIN?
	CW Spot Level - no hamlib support - RIG_LEVEL_CW_SPOT?
	Enable/Disable Amplifier keying loop - no hamlib support - RIG_FUNC_AMP?
