Feature/client server demo

[martindevans]

Initial version of networking system.

• New packet types can be defined as simple structs in packets.rs
• Serialization of packets is done with msgpack, changing to something else is a one line change

On the client:

• polls for streams
• publishes received packets as ECS events
• takes ECS events and sends them as packets
• creates an Entity with a Connection component

Server does all this, and also:

• polls for connections

Note: This has not yet been fully tested due to fun with certificates.

[martindevans]

Latest commit has added an option to totally bypass certs and just accept anything as a valid cert. This means you can now test with:

cargo run --bin server -- --cert "./certs/cert.pem" --key "./certs/key.pem" cargo run --bin client -- --cert "./certs/cert.pem" --url "quic://localhost:4433" --accept_any

[martindevans]

Demo video: https://static.placeholder-software.co.uk/gallery/bounded-planet/2020-09-25_18-52-45.webm