XDAG Refactor Advice

[LucasMLK]

Is your feature request related to a problem? Please describe.
I think the code of the xdag needs to be refactor，it's too difficult to maintain and reading
and needs develop guide for develper to start working.

Describe the solution you'd like
Networking:
Nanomsg is a socket library that provides several common communication modes in order to make the network layer fast, scalable, and easy to use. Implemented in C and suitable for a wide range of operating systems, almost no dependency.

Libevent is a lightweight, open source, high-performance event notification library written in C. It has several highlights: event-driven, high-performance, lightweight, and focused on the network.

Above two library is very popular and stable for networking refactor.

Storage:
rocksdb is a much better for sotre data ,and it's very stable for store account and utxo value.

Testing:
XDAG need Unit test framework or tools ,such as Gtest or other?