feature(network): Create a new `network` module with `client` and `protocol` submodules

Relates to #103 (closed)

1. Create a new network module with client and protocol submodules
2. Code in these modules is mostly copied net_box with minimal changes
3. Code in new modules was split so that protocol is independent from tarantool symbols
4. The only part not added to new fork is schema as it was decided to be left out

The idea is to create an experimental fork of net_box and continue cutting the client to gradually move things into protocol following a sans-io based design. In the process async will be introduced and code will be refactored to follow more Rust(y) conventions.