gr_autolink

This is an adaptation of the extraction of the `auto_link` method from rails that is the rails_autolink gem. The `auto_link` method was removed from Rails in version Rails 3.1. This gem is meant to bridge the gap for people migrating...and behaves a little differently from the parent gem we forked from: * performs html-escaping of characters such as '&' in strings that are getting linkified if the incoming string is not html_safe? * retains html-safety of incoming string (if input string is unsafe, will return unsafe and vice versa) * fixes at least one bug: (<img src="http://some.u.rl"> => <img src="<a href="http://some.u.rl">http://some.u.rl</a>">) though can't imagine this is intended behavior, also have trouble believing that this was an open bug in rails...