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/lodash/_asciiSize.js

@@ -0,0 +1,12 @@
+var baseProperty = require('./_baseProperty');
+
+/**
+ * Gets the size of an ASCII `string`.
+ *
+ * @private
+ * @param {string} string The string inspect.
+ * @returns {number} Returns the string size.
+ */
+var asciiSize = baseProperty('length');
+
+module.exports = asciiSize;