Adding \wcf\system\Regex

Adding \wcf\system\Regex

That way we can typehint regexes and have object-oriented access on regexes.

There is no longer a need to add or escape the delimiters, this is all done by the Regex-class.
The modifiers are added via a bitmask as the second parameter:
	Valid modifiers are:
		Regex::CASE_INSENSITIVE (add i)
		Regex::EVAL_REPLACEMENT (add e)
		Regex::UNGREEDY (add U)
		Regex::NO_ANALYSE (don't add s)

Usage:

```
$regex = new Regex('^http(s)?://(www\.)woltlab\.(com|de|info)/', Regex::CASE_INSENSITIVE);
var_dump($regex->match('http://www.woltlab.com/pluginstore/')); // int(1)
var_dump($regex->getMatches()); // array with all matched substrings

var_dump(Regex::compile('[a-z]')->replace('asdf345', '')); // string(3) "345"
var_dump(Regex::compile('[a-z]')->replace('asdf345', new Callback(function ($matches) {
	return 'x';
})); // string(7) "xxxx345"
```