Function _randomCode

Generate a random string from the given array of letters.

Package: PHPLucidFrame\Core
Copyright: Copyright (c), PHPLucidFrame.
License: MIT License This source file is subject to the MIT license that is bundled with this source code in the file LICENSE
Author: Sithu sithu@phplucidframe.com
Located at helpers/utility_helper.php

Parameters summary
`integer`	`$length = 5`	The length of required random string
`array`	`$letters = array()`	<p>Array of letters from which randomized string is derived from. Default is a to z and 0 to 9.</p>
`string`	`$prefix = ''`	Prefix to the generated string

Return value summary
`string`	The random string of requried length