Add picocalc stm32 i2c keyboard code

Code/picocalc_keyboard/fifo.h

@@ -0,0 +1,18 @@
+#ifndef FIFO_H
+#define FIFO_H
+
+#include "keyboard.h"
+
+struct fifo_item {
+  char key;
+  enum key_state state;
+};
+
+uint8_t fifo_count(void);
+void fifo_flush(void);
+bool fifo_enqueue(const struct fifo_item item);
+void fifo_enqueue_force(const struct fifo_item item);
+struct fifo_item fifo_dequeue(void);
+
+
+#endif