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/@babel/parser/README.md

@@ -0,0 +1,19 @@
+# @babel/parser
+
+> A JavaScript parser
+
+See our website [@babel/parser](https://babeljs.io/docs/en/next/babel-parser.html) for more information or the [issues](https://github.com/babel/babel/issues?utf8=%E2%9C%93&q=is%3Aissue+label%3A%22pkg%3A+parser+%28babylon%29%22+is%3Aopen) associated with this package.
+
+## Install
+
+Using npm:
+
+```sh
+npm install --save-dev @babel/parser
+```
+
+or using yarn:
+
+```sh
+yarn add @babel/parser --dev
+```