implement basic clientside RPC infrastructure

and provide a basic example for testing it

www/examples/rpc/main.js

@@ -0,0 +1,35 @@
+require.config({ paths: { 'json.sortify': '/bower_components/json.sortify/dist/JSON.sortify' } });
+define([
+    '/common/cryptpad-common.js',
+    '/common/rpc.js',
+    '/bower_components/jquery/dist/jquery.min.js',
+], function (Cryptpad, RPC) {
+    var $ = window.jQuery;
+    var APP = window.APP = {
+        Cryptpad: Cryptpad,
+    };
+
+    $(function () {
+        Cryptpad.ready(function (err, env) {
+            var network = Cryptpad.getNetwork();
+            var rpc = RPC.create(network); // TODO signing key
+
+            var payload = {
+                a: Math.floor(Math.random() * 1000),
+                b: 7,
+            };
+
+            // console.log(payload);
+            rpc.send('ECHO', payload, function (e, msg) {
+                if (e) { return void console.error(e); }
+                console.log(msg);
+            });
+
+            // test a non-existent RPC call
+            rpc.send('PEWPEW', ['pew'], function (e, msg) {
+                if (e) { return void console.error(e); }
+                console.log(msg);
+            });
+        });
+    });
+});