Wiki Link Substitution and non-alphanumeric character in display text.

We are using ponydocs for localization(Ex. http://docs.genesys.com/i18n/DEU/Documentation/IW/8.5.1/Help/Welcome) and noticed that ponydocs  wikilinks with non-alphanumeric characters were breaking. Implemented this fix to support non-alphanumeric characters in the display text.

Change based on MediaWiki's regex in parser.php file:

```php
if ( !$tc ) {
			$tc = Title::legalChars() . '#%';
			# Match a link having the form [[namespace:link|alternate]]trail
			$e1 = "/^([{$tc}]+)(?:\\|(.+?))?]](.*)\$/sD";
			# Match cases where there is no "]]", which might still be images
			$e1_img = "/^([{$tc}]+)\\|(.*)\$/sD";
		}
```