Optimize the overhead of the tag message of the request

For now, every request the client sent consists of a tag message(TMessage) and the API arguments.

This tag message includes the API name(method name), message type and a sequence ID.

Compare to the API arguments which usually are some structure data like integers, the tag message will cause a lot of overhead because of the API name string.

For example, assume we have an API like this in Java:

int getSomeEntityById(int id);

The the tag message will takes len("getSomeEntityById") + 1 + 4 = 22 bytes and the API arguments only takes 4 bytes.

Even worse if we support multiplexing, because we need append additional service name at the beginning of the API name.

So shall we assign an ID to each API like struct's every property has an ID? Then we can avoid using the verbose string names.