[FEATURE REQUEST] Add zpp_bits adapter

[jharmer95]

Feature Request: Add zpp_bits adapter

Brief Summary of Request

zpp_bits is a very fast (but simple) binary serialization library and could be a nice addition

What Is The Value Added With This Feature

Access to another serialization library, option for faster serialization

Possible Implementation

Add a rpc_zpp.hpp file to the adapters directory.

Other Details

NOTE: zpp_bits requires C++20, so this adapter would be optional (not included by default) until the C++20 branch of rpc.hpp