board/sg-frame.c: Add "sg" framing support

board/sg-frame.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <windows.h>
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "hook/iobuf.h"
+
+HRESULT sg_frame_decode(
+        struct iobuf *dest,
+        const uint8_t *bytes,
+        size_t nbytes);
+
+HRESULT sg_frame_encode(struct iobuf *dest, const void *ptr, size_t nbytes);