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

protocol/usb_hid/NullSerial.cpp

@@ -0,0 +1,44 @@
+#include "USBAPI.h"
+
+
+void NullSerial::begin(uint16_t baud_count)
+{
+}
+
+void NullSerial::end(void)
+{
+}
+
+void NullSerial::accept(void)
+{
+}
+
+int NullSerial::available(void)
+{
+    return 0;
+}
+
+int NullSerial::peek(void)
+{
+    return -1;
+}
+
+int NullSerial::read(void)
+{
+    return -1;
+}
+
+void NullSerial::flush(void)
+{
+}
+
+size_t NullSerial::write(uint8_t c)
+{
+    return 1;
+}
+
+NullSerial::operator bool() {
+    return true;
+}
+
+NullSerial Serial;