Moved wallet to separate file.

wallet/index.js

@@ -0,0 +1,15 @@
+'use strict';
+
+var Wallet = require('./wallet');
+var HDNode = require('./hdnode');
+var SigningKey = require('./signing-key');
+
+module.exports = {
+    HDNode: HDNode,
+    Wallet: Wallet,
+
+    // Do we need to expose this at all?
+    _SigningKey: SigningKey,
+}
+
+require('ethers-utils/standalone.js')(module.exports);