This is a first cut at a simple MIDI output port.

	open/close
	close ensureOpen openOnPortNumber: portNumber

	output
	midiCmd:channel:byte: midiCmd:channel:byte:byte: midiOutput:

	primitives
	primMIDIClosePort: primMIDIOpenPort:readSemaIndex:interfaceClockRate: primMIDIReadPort:into: primMIDIWritePort:from:at:

	instance creation
	openDefault openOnPortNumber:

	primitives
	primPortCount primPortDirectionalityOf: primPortNameOf:

	utilities
	closeAllPorts inputPortNumFromUser midiIsSupported outputPortNumFromUser portDescription:

	input	top
	bufferTimeStampFrom: Return the timestamp from the given MIDI input buffer. Assume the given buffer is at least 4 bytes long.
	flushInput Read any lingering MIDI data from this port's input buffer.
	readInto: Read any data from this port into the given buffer.

	open/close	top
	close Close this MIDI port.
	ensureOpen Make sure this MIDI port is open. It is good to call this before starting to use a port in case an intervening image save/restore has caused the underlying hardware port to get closed.
	openOnPortNumber: Open this MIDI port on the given port number.
	portNumber Answer my port number.

	output	top
	midiCmd:channel:byte: Immediately output the given MIDI command with the given channel and argument byte to this MIDI port. Assume that the port is open.
	midiCmd:channel:byte:byte: Immediately output the given MIDI command with the given channel and argument bytes to this MIDI port. Assume that the port is open.
	midiOutput: Output the given bytes to this MIDI port immediately. Assume that the port is open.

	primitives	top
	primMIDIClosePort: Close the given MIDI port. Don't fail if port is already closed.
	primMIDIOpenPort:readSemaIndex:interfaceClockRate: Open the given MIDI port. If non-zero, readSemaIndex specifies the index in the external objects array of a semaphore to be signalled when incoming MIDI data is available. Not all platforms support signalling the read semaphore. InterfaceClockRate specifies the clock rate of the external MIDI interface adaptor on Macintosh computers; it is ignored on other platforms.
	primMIDIReadPort:into: Read any available MIDI data into the given buffer (up to the size of the buffer) and answer the number of bytes read.
	primMIDIWritePort:from:at: Queue the given data to be sent through the given MIDI port at the given time. If midiClockValue is zero, send the data immediately.

	class initialization	top
	initialize SimpleMIDIPort initialize

	instance creation	top
	openDefault Answer a new instance of me opened on the default MIDI port.
	openOnPortNumber: Answer a new instance of me for the given MIDI port number.

	primitives	top
	primPortCount Answer the number of MIDI ports supported by this platform, or zero if this primitive is not implemented.
	primPortDirectionalityOf: Answer the platform-specific name for the given MIDI port.
	primPortNameOf: Answer the platform-specific name for the given MIDI port.

	utilities	top
	closeAllPorts Close all MIDI ports.
	inputPortNumFromUser Prompt the user for a MIDI input port. Answer a port number, or nil if the user does not select a port or if MIDI is not supported on this platform.
	midiIsSupported Answer true if this platform supports MIDI.
	outputPortNumFromUser Prompt the user for a MIDI output port. Answer a port number, or nil if the user does not select a port or if MIDI is not supported on this platform.
	portDescription: Answer a string indicating the directionality of the given MIDI port.