feat: (BREAKING CHANGE) overhaul libp2p config and constructor

* docs: update chat example and add info to its readme
* docs: update echo example
* docs: update libp2p in browser example
* docs: update pubsub example
* docs: update peer and content routing examples
* docs: update discovery mechanisms example
* docs: update encrypted comms example
* docs: update protocol and stream muxing example
* feat: add config validation
* test: update CI configs, use only node 8

test/utils/echo.js

@@ -0,0 +1,10 @@
+/* eslint-env mocha */
+'use strict'
+
+const pull = require('pull-stream')
+
+function echo (protocol, conn) {
+  pull(conn, conn)
+}
+
+module.exports = echo