Update Proposed API

[anssiko]

• Break sample code into smaller blocks and add descriptions
• API design changes:
  • p2pManager -> p2p
  • peerA and peerB naming
  • peer.send() returns a promise
  • try-catch error handling (promise always coerced to true)
  • remove if (p2pSession) check

[ibelem]

Thanks @anssiko for the clearer code structure and code flow for explainer readers and reviewers!