Add USB HID(host) protocol.(not finished)

protocol/usb_hid/USBAPI.h

@@ -0,0 +1,22 @@
+/*
+ * Override original arduino USBAPI.h.
+ */
+#include <stdint.h>
+#include "Stream.h"
+
+
+class NullSerial : public Stream
+{
+public:
+	void begin(uint16_t baud_count);
+	void end(void);
+
+	virtual int available(void);
+	virtual void accept(void);
+	virtual int peek(void);
+	virtual int read(void);
+	virtual void flush(void);
+	virtual size_t write(uint8_t);
+	operator bool();
+};
+extern NullSerial Serial;