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/trim-right/readme.md

@@ -0,0 +1,30 @@
+# trim-right [![Build Status](https://travis-ci.org/sindresorhus/trim-right.svg?branch=master)](https://travis-ci.org/sindresorhus/trim-right)
+
+> Similar to [`String#trim()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/Trim) but removes only whitespace on the right
+
+
+## Install
+
+```
+$ npm install --save trim-right
+```
+
+
+## Usage
+
+```js
+var trimRight = require('trim-right');
+
+trimRight('  unicorn  ');
+//=> '  unicorn'
+```
+
+
+## Related
+
+- [`trim-left`](https://github.com/sindresorhus/trim-left) - Similar to `String#trim()` but removes only whitespace on the left
+
+
+## License
+
+MIT © [Sindre Sorhus](http://sindresorhus.com)