Add DHT packet parsing

[zetok]

Add parsing for packets (add types if don't exist already and implement ToBytes + FromBytes traits for them):

• | 0x00 | Ping Request
• | 0x01 | Ping Response
• | 0x02 | Nodes Request
• | 0x04 | Nodes Response
• | 0x18 | Cookie Request
• | 0x19 | Cookie Response
• | 0x1a | Crypto Handshake
• | 0x1b | Crypto Data
• | 0x20 | DHT Request
• | 0x21 | LAN Discovery
• | 0x80 | Onion Request 0
• | 0x81 | Onion Request 1
• | 0x82 | Onion Request 2
• | 0x83 | Announce Request
• | 0x84 | Announce Response
• | 0x85 | Onion Data Request
• | 0x86 | Onion Data Response
• | 0x8c | Onion Response 3
• | 0x8d | Onion Response 2
• | 0x8e | Onion Response 1
• | 0xf0 | Bootstrap Info

DhtRequest packets are partially supported, in order to support them fully Onion packets also need to have parsing implemented.

https://zetok.github.io/tox-spec/#packet-kind

[Roman]

Closed in favour of https://github.com/tox-rs/tox/