Interaction with Coordinator module

[elmigranto]

PR: #21

[elmigranto]

We'll have 2 types of notifications:

• leave — someone left a game;
• join — someone joined a game.

Both will have common notification.data:

{ "game": {
    "id": String
    "type": String
    "players": [String]
  }

  "player": String  // username of a person who left/joined
  "reason": String  // not sure, "resign" for leave, what about joininng?
}

[j3k0]

That's it. There's no reason for join, and it's optional for leave.

[elmigranto]

Closing this, #21 is ready.