Start running a digital output waveform playback schedule. The actual hardware
schedule will be initiated by the next RegWr* command, and then the first
waveform sample will hit the digital outputs after the scheduleOnset specified
Note that every call to StartDoutSchedule must be preceeded by a call to
SetDoutSchedule (ie: multiple calls to StartDoutSchedule each require their own
call to SetDoutSchedule)).
See DatapixxDout*Demo files for examples.