Add TOML config support for the client

[Skeletrox]

The client should be able to use a separate config file for its behavior, also as a TOML file.

[Skeletrox]

Implemented — the client reads its configuration from client_config.toml using the toml and serde crates. The config file supports [server_addr] (ip, port) and [log_info] (log_file) sections.