Added USB Virtual Serial support

tmk_core/common/virtser.h

@@ -0,0 +1,10 @@
+#ifndef _VIRTSER_H_
+#define _VIRTSER_H_
+
+/* Define this function in your code to process incoming bytes */
+void virtser_recv(const uint8_t ch);
+
+/* Call this to send a character over the Virtual Serial Device */
+void virtser_send(const uint8_t byte);
+
+#endif