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/pascalcase/index.js

@@ -0,0 +1,21 @@
+/*!
+ * pascalcase <https://github.com/jonschlinkert/pascalcase>
+ *
+ * Copyright (c) 2015, Jon Schlinkert.
+ * Licensed under the MIT License.
+ */
+
+function pascalcase(str) {
+  if (typeof str !== 'string') {
+    throw new TypeError('expected a string.');
+  }
+  str = str.replace(/([A-Z])/g, ' $1');
+  if (str.length === 1) { return str.toUpperCase(); }
+  str = str.replace(/^[\W_]+|[\W_]+$/g, '').toLowerCase();
+  str = str.charAt(0).toUpperCase() + str.slice(1);
+  return str.replace(/[\W_]+(\w|$)/g, function (_, ch) {
+    return ch.toUpperCase();
+  });
+}
+
+module.exports = pascalcase;