[Yunq] Move serialization to yunq library.

lib/yunq/yunq.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <stdint.h>
+
+namespace yunq {
+
+struct MessageHeader {
+  uint32_t ident;
+  uint32_t core_length;
+  uint32_t length;
+  uint32_t crc32;
+  uint64_t options;
+} __attribute__((packed));
+
+const uint64_t kHeaderSize = 24;  // 4x uint32, 1x uint64
+
+struct ExtensionPointer {
+  uint32_t offset;
+  uint32_t length;
+};
+
+}  // namespace yunq