New "browse" UI

Also, separated out browse, ?meta, and ?module request handlers.

Fixes #82

modules/client/browse.js

@@ -0,0 +1,8 @@
+import React from 'react';
+import ReactDOM from 'react-dom';
+
+import App from './browse/App.js';
+
+const props = window.__DATA__ || {};
+
+ReactDOM.hydrate(<App {...props} />, document.getElementById('root'));