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/is-wsl/readme.md

@@ -0,0 +1,28 @@
+# is-wsl [![Build Status](https://travis-ci.org/sindresorhus/is-wsl.svg?branch=master)](https://travis-ci.org/sindresorhus/is-wsl)
+
+> Check if the process is running inside [Windows Subsystem for Linux](https://msdn.microsoft.com/commandline/wsl/about) (Bash on Windows)
+
+Can be useful if you need to work around unimplemented or buggy features in WSL.
+
+
+## Install
+
+```
+$ npm install --save is-wsl
+```
+
+
+## Usage
+
+```js
+const isWsl = require('is-wsl');
+
+// When running inside Windows Subsystem for Linux
+console.log(isWsl);
+//=> true
+```
+
+
+## License
+
+MIT © [Sindre Sorhus](https://sindresorhus.com)