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/remove-trailing-separator/readme.md

@@ -0,0 +1,51 @@
+# remove-trailing-separator
+
+[![NPM version][npm-img]][npm-url] [![Build Status: Linux][travis-img]][travis-url] [![Build Status: Windows][appveyor-img]][appveyor-url] [![Coverage Status][coveralls-img]][coveralls-url]
+
+Removes all separators from the end of a string.
+
+## Install
+
+```
+npm install remove-trailing-separator
+```
+
+## Examples
+
+```js
+const removeTrailingSeparator = require('remove-trailing-separator');
+
+removeTrailingSeparator('/foo/bar/')   // '/foo/bar'
+removeTrailingSeparator('/foo/bar///') // '/foo/bar'
+
+// leaves only/last separator
+removeTrailingSeparator('/')    // '/'
+removeTrailingSeparator('///')  // '/'
+
+// returns empty string
+removeTrailingSeparator('') // ''
+```
+
+## Notable backslash, or win32 separator behavior
+
+`\` is considered a separator only on WIN32 systems. All POSIX compliant systems
+see backslash as a valid file name character, so it would break POSIX compliance
+to remove it there.
+
+In practice, this means that this code will return different things depending on
+what system it runs on:
+
+```js
+removeTrailingSeparator('\\foo\\')
+// UNIX  => '\\foo\\'
+// WIN32 => '\\foo'
+```
+
+[npm-url]: https://npmjs.org/package/remove-trailing-separator
+[npm-img]: https://badge.fury.io/js/remove-trailing-separator.svg
+[travis-url]: https://travis-ci.org/darsain/remove-trailing-separator
+[travis-img]: https://travis-ci.org/darsain/remove-trailing-separator.svg?branch=master
+[appveyor-url]: https://ci.appveyor.com/project/darsain/remove-trailing-separator/branch/master
+[appveyor-img]: https://ci.appveyor.com/api/projects/status/wvg9a93rrq95n2xl/branch/master?svg=true
+[coveralls-url]: https://coveralls.io/github/darsain/remove-trailing-separator?branch=master
+[coveralls-img]: https://coveralls.io/repos/github/darsain/remove-trailing-separator/badge.svg?branch=master