Provide way of selecting user profile field to replace default username

This is a great module. The only improvement I can suggest at this point is to add a way to make the !name token take the value of something other than the username, since usernames are not always "fully qualified", i.e., my name on a site might be markj but my real name is Mark Jordan. Including an admin setting to define which field in the profile module is the one to use, for example, might be a way around this. I haven't looked at the code yet but if it looks fairly straightforward I might be able to provide a patch to do this, if you're interested.