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/to-fast-properties/readme.md

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+# to-fast-properties [![Build Status](https://travis-ci.org/sindresorhus/to-fast-properties.svg?branch=master)](https://travis-ci.org/sindresorhus/to-fast-properties)
+
+> Force V8 to use fast properties for an object
+
+[Read more.](http://stackoverflow.com/questions/24987896/)
+
+Use `%HasFastProperties(object)` and `--allow-natives-syntax` to check whether an object already has fast properties.
+
+
+## Install
+
+```
+$ npm install --save to-fast-properties
+```
+
+
+## Usage
+
+```js
+const toFastProperties = require('to-fast-properties');
+
+const obj = {
+	foo: true,
+	bar: true
+};
+
+delete obj.foo;
+// `obj` now has slow properties
+
+toFastProperties(obj);
+// `obj` now has fast properties
+```
+
+
+## License
+
+MIT © Petka Antonov, John-David Dalton, Sindre Sorhus