Feature: Server implementation in Rust

[crapStone]

This PR adds a server implementation in Rust that tries to follow the original implementation closely, but differs in some ways because of the language restrictions of Rust.

TODOs:

• [x] header callback
• [ ] create and add Peer to map
• [ ] handle Peer connecting
• [ ] listen for and handle client messages
• [ ] create heartbeat timer

closes #512