add USB temlpate for F303

F3:F303/USB_template/ringbuffer.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include <stm32f3.h>
+
+typedef struct{
+    uint8_t *data;      // data buffer
+    const int length;   // its length
+    int head;           // head index
+    int tail;           // tail index
+} ringbuffer;
+
+int RB_read(ringbuffer *b, uint8_t *s, int len);
+int RB_readto(ringbuffer *b, uint8_t byte, uint8_t *s, int len);
+int RB_hasbyte(ringbuffer *b, uint8_t byte);
+int RB_write(ringbuffer *b, const uint8_t *str, int l);
+int RB_datalen(ringbuffer *b);
+void RB_clearbuf(ringbuffer *b);