libmidi++: add the hitherto unknown and unsupported MIDI "tick" message

See http://midi.teragonaudio.com/tech/midispec/tick.htm

libs/midi++2/midi++/parser.h

@@ -102,6 +102,7 @@ class LIBMIDIPP_API Parser {
 	ZeroByteSignal        eox;
 
 	TimestampedSignal     timing;
+	TimestampedSignal     tick; /* rarely seen in the wild */
 	TimestampedSignal     start;
 	TimestampedSignal     stop;
 	TimestampedSignal     contineu;  /* note spelling */

libs/midi++2/midi++/types.h

@@ -54,6 +54,7 @@ namespace MIDI {
 	    tune = 0xF6,
 	    eox = 0xF7,
 	    timing = 0xF8,
+	    tick = 0xF9,
 	    start = 0xFA,
 	    contineu = 0xFB, /* note spelling */
 	    stop = 0xFC,

libs/midi++2/parser.cc

@@ -551,6 +551,9 @@ Parser::realtime_msg(unsigned char inbyte)
 	case 0xf8:
 		timing (*this, _timestamp);
 		break;
+	case 0xf9:
+		tick (*this, _timestamp);
+		break;
 	case 0xfa:
 		start (*this, _timestamp);
 		break;