refactor(docs): async await version of examples/echo (#483)

* fix: performance bottleneck in stat.js (#463)

Array.shift seems to be very slow, perhaps linear, on some
engines, resulting in  _update consuming a lot of CPU.

* docs(fix): correct docs and example for pnet (#464)

* docs(fix): correct docs and example for pnet

* docs(fix): correct pnet docs

* docs(fix): update README.md language (#468)

* docs: reciprocate (#474)

* docs(example): fix ipfs cat (#475)

`ipfs.files.cat` is incorrect. the correct function is `ipfs.cat`

* fix: async await examples/echo

* fix: examples readme typos (#481)

* fix: simplify libp2p bundle for echo example

examples/echo/src/libp2p-bundle.js

@@ -1,41 +1,12 @@
 'use strict'
 
 const TCP = require('libp2p-tcp')
-const MulticastDNS = require('libp2p-mdns')
 const WS = require('libp2p-websockets')
-const Bootstrap = require('libp2p-bootstrap')
-const spdy = require('libp2p-spdy')
-const KadDHT = require('libp2p-kad-dht')
 const mplex = require('libp2p-mplex')
 const secio = require('libp2p-secio')
 const defaultsDeep = require('@nodeutils/defaults-deep')
 const libp2p = require('../../..')
 
-function mapMuxers (list) {
-  return list.map((pref) => {
-    if (typeof pref !== 'string') {
-      return pref
-    }
-    switch (pref.trim().toLowerCase()) {
-      case 'spdy': return spdy
-      case 'mplex': return mplex
-      default:
-        throw new Error(pref + ' muxer not available')
-    }
-  })
-}
-
-function getMuxers (muxers) {
-  const muxerPrefs = process.env.LIBP2P_MUXER
-  if (muxerPrefs && !muxers) {
-    return mapMuxers(muxerPrefs.split(','))
-  } else if (muxers) {
-    return mapMuxers(muxers)
-  } else {
-    return [mplex, spdy]
-  }
-}
-
 class Node extends libp2p {
   constructor (_options) {
     const defaults = {
@@ -44,29 +15,8 @@ class Node extends libp2p {
           TCP,
           WS
         ],
-        streamMuxer: getMuxers(_options.muxer),
-        connEncryption: [ secio ],
-        peerDiscovery: [
-          MulticastDNS,
-          Bootstrap
-        ],
-        dht: KadDHT
-      },
-      config: {
-        peerDiscovery: {
-          mdns: {
-            interval: 10000,
-            enabled: false
-          },
-          bootstrap: {
-            interval: 10000,
-            enabled: false,
-            list: _options.bootstrapList
-          }
-        },
-        dht: {
-          kBucketSize: 20
-        }
+        streamMuxer: [ mplex ],
+        connEncryption: [ secio ]
       }
     }