Added support for Contains clause...

Added support for Contais clause, as mentioned in this article:

http://blog.walteralmeida.com/2010/05/advanced-linq-dynamic-linq-library-add-support-for-contains-extension-.html

O followed the steps mentioned, however, I still had to do some additional coding to make it work.
I have used this code and I think this would be a nice to contribute back to the original project :)