Added preg_match() for generating link for 'uses constant'

At the moment in some cases Kohana_Kodoc::link_class_member() generates incorrect links.
For example links Route::REGEX_ESCAPE, Route::REGEX_SEGMENT are incorrect: http://kohanaframework.org/3.3/guide-api/Route#compile

I think that would be a bit correctly, if we assume the constants as defined in http://www.php.net/manual/en/language.constants.php, and eliminating the lowercase letters from the $matches

(Sorry for my english)