Implement webrtc in js-libp2p

[ddimaria]

Tasks

• Skeletons for Transport, Connection, and Stream implementations
• SDP munging
• SDP creation
• Implement Transport.dial
• Implement remainder of Transport
• Implement Connection.newStream
• Implement remainder of Connection
• Implement Stream.source
• Implement Stream.sink
• Implement remainder of Stream
• Fill out README.md and any other worthwhile documentation
• Unit test SDP utilities
• Unit test Transport
• Unit test Connection
• Unit test Stream
• Custom error types
• Fix lint errors in develop