Move event packet type declaration into a separate header (#47)

* refactor: Move event packet declaration into a separate header

This would allow 3rd party code to work with this data type
without including the whole interface code, which is
environment-specific.

Author: Francois Best

src/MIDIUSB.h

@@ -18,13 +18,7 @@
 #error MIDIUSB can only be used with an USB MCU.
 #endif
 
-typedef struct
-{
-	uint8_t header;
-	uint8_t byte1;
-	uint8_t byte2;
-	uint8_t byte3;
-}midiEventPacket_t;
+#include "MIDIUSB_Defs.h"
 
 #if defined(ARDUINO_ARCH_AVR)
 

src/MIDIUSB_Defs.h

@@ -0,0 +1,10 @@
+#pragma once
+#include <stdint.h>
+
+typedef struct
+{
+	uint8_t header;
+	uint8_t byte1;
+	uint8_t byte2;
+	uint8_t byte3;
+} midiEventPacket_t;