v0.1.2: More robust and complete

• More loggings.
• A more complete Mplex.
  • Detect disconnection from peers.
• Align Swarm and BasicHost structure with Go.
  • Multiselect is moved to BasicHost.
  • Swarm is able to detect and remove disconnected peers.
• A more complete secio.
• More exception handling.
• Add Identify and Ping protocols. Besides, they are set as the default protocols in BasicHost.
• Detect dead peers in Pubsub.