Function _shorten
Shorten a string for the given length
		
		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
Located at helpers/utility_helper.php
	
	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
Located at helpers/utility_helper.php
string | 
		$str | 
		A plain text string to be shortened | 
integer | 
		$length = 50 | 
		The character count | 
string | 
		$trail = '...' | 
		To append <code>...</code> or not. <code>null</code> to not show | 
			string
		 | 
		The shorten text string |