add bitcore.KeyModule back as deprecated

This will allow bitcore.KeyModule to work with existing code, but it prints out
a message that it is deprecated.

bitcore.js

@@ -31,6 +31,10 @@ requireWhenAccessed('Block', './Block');
 requireWhenAccessed('ScriptInterpreter', './ScriptInterpreter');
 requireWhenAccessed('Bloom', './Bloom');
 requireWhenAccessed('Key', './Key');
+Object.defineProperty(module.exports, 'KeyModule', {get: function() {
+  console.log('KeyModule is deprecated.');
+  return require('bindings')('KeyModule');
+}});
 requireWhenAccessed('SINKey', './SINKey');
 requireWhenAccessed('SIN', './SIN');
 requireWhenAccessed('PrivateKey', './PrivateKey');