Introduce formal generators.

Introduce a shallow hierarchy of simple generator classes, collecting
common functionality and allowing for future snap-in generator
replacement. Use John Resig's "class"-based inheritance per
http://ejohn.org/blog/simple-javascript-inheritance/.

src/gen/text-generator.js

@@ -0,0 +1,15 @@
+/**
+Plain text resume generator for FluentCV.
+@license Copyright (c) 2015 by James M. Devlin. All rights reserved.
+*/
+
+var TemplateGenerator = require('./template-generator');
+var TextGenerator = TemplateGenerator.extend({
+
+  init: function(){
+    this._super( 'txt' );
+  },
+
+});
+
+module.exports = TextGenerator;