nyud_appender()

Hi there!

I saw your post on /r/OpenDirectories and wanted to contribute.  Someone in the comments mentioned a desire for the bot to append .nyud.net to URLs, so I added a function which does that.  

This is my first time submitting a pull request, and I had to brush up on Git to do all of this.  If I've made any mistakes, I apologize, and please don't hesitate to point them out.

What I have not done is update oBot.run() so as to actually post the new URL.  I don't mind adding this functionality myself, but I don't have much experience with PRAW, and didn't have the time today to set it up to experiment with posting the comment.

Thanks, and if you have any questions, comments, or suggestions, I'm all ears.