Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/handlebars/lib/index.js

@@ -0,0 +1,25 @@
+// USAGE:
+// var handlebars = require('handlebars');
+/* eslint-disable no-var */
+
+// var local = handlebars.create();
+
+var handlebars = require('../dist/cjs/handlebars')['default'];
+
+var printer = require('../dist/cjs/handlebars/compiler/printer');
+handlebars.PrintVisitor = printer.PrintVisitor;
+handlebars.print = printer.print;
+
+module.exports = handlebars;
+
+// Publish a Node.js require() handler for .handlebars and .hbs files
+function extension(module, filename) {
+  var fs = require('fs');
+  var templateString = fs.readFileSync(filename, 'utf8');
+  module.exports = handlebars.compile(templateString);
+}
+/* istanbul ignore else */
+if (typeof require !== 'undefined' && require.extensions) {
+  require.extensions['.handlebars'] = extension;
+  require.extensions['.hbs'] = extension;
+}