T1: Update Peer List

[memoriesadrift]

Blocked by #4, #5

Description

• Upon connection with any peer (initiated either by your node or the peer), send a "getpeers" message immediately after the "hello" message.
• On receiving a "peers" message from a connected peer, update your list of discovered peers.
• On receiving a "getpeers" message from a connected peer, send a "peers" message with your list of peers. Note that by specification of the protocol, a "peers" message must not contain more than 30 peers. If you have more than 30 peer stored, devise a policy on which 30 you send over the network.
• Devise a policy to decide which peers to connect to and how many to connect to. We suggest to connect to just a few nodes, and not all of them.

Scope

1. Send getpeers message after establishing a handshake
2. Send peers message when receiving getpeers message from a known host
3. Devise a policy on which nodes to connect to (should be more robust, akin to a final implementation, imo)
4. Devise a method of choosing 30 peers to send if over 30 peers stored (can probably be a placeholder strategy for now)

[memoriesadrift]

1 and 2 are covered by #12, they were relatively trivial.

For 2. add the limitation of the message having to be received by a known (and handshaked) host and just implement 3. and 4.

[memoriesadrift]

Addition from re-read of spec:

A node should include itself in the list of peers at the first position if it is listening for incoming connections. Your node should always listen for and accept new incoming connections.