Peer group feature

[tok-kkk]

• Introduce PeerGroup which is a group of PeerIDs. When sending messages, you can specify the target nodes by a PeerGroupID.
• Add unit tests for each package and an integration tests in the Peer package
• Set up circleCI and coverall so that we can't ignore fail CI anymore.
• Fix some issues discovered by the tests.

[tok-kkk]

Have made changes according to the comments above, please have a another review @loongy.

For the handshake process , I change the RSA key to ECDSA for encryption and decryption
Now the handshake process is:
1. Client generates a new ECDSA key and writes it to the server.
2. Server verifies the key -> generates a new ECDSA key -> writes it to the client
3. Client verifies the key -> generates a new session key -> encrypts it with Server's ECDSA key - > sends to server
4. Server decrypted the session key -> generates a new session key -> encrypts it with Client's ECDSA key - > sends to client
5. Client decrypted the session key and use the XOR result of both session keys to creating a session

Not sure if the client needs to respond to the server to confirm it gets the server's session key ?

[loongy]

@tok-kkk no need for explicit confirmation. The first non-handshake message to be sent on the wire is an implicit confirmation.

[loongy]

Server verifies the key

@tok-kkk what do you mean by this?

[tok-kkk]

@loongy It sends the new ECDSA key along with a signature(signed by the key which generates his PeerID). So the server can extract the PeerID from the signature and verifies the sender is valid.