Few more possible regular expressions to check checkbox is checked

I added a couple of regular expressions that helps the user to check if a checkbox is checked or not on a page. 

Committed here - <a href="https://github.com/kssundar/MinkExtension/commit/de37a1a1deafaae859943a728fe2b24496321d6b">de37a1a</a>

Is it worth?