Pull Go examples into docs site

[yusefnapora]

This covers the go part of #29

The idea is to pull the examples from https://github.com/libp2p/go-libp2p-examples into the docs site, ideally using an automated process to pull in the narrative and code samples from the example READMEs. May take some rewriting / tweaking of the readmes

• The libp2p 'host'
• Building an http proxy with libp2p
• An echo host
• Multicodecs with protobufs
• P2P chat application
• P2P chat application w/ rendezvous peer discovery
• P2P chat application with peer discovery using mdns

[p-shahi]

closing #38 (comment)