[Grace-core] Singleton types

[James Noble]

> The Grace spec in section 11.10 specifies that any object may be used as the name of a singleton type without further annotation.  In the first draft of the SIGCSE paper I had written that for object obj as "obj.type" rather than just "obj".  Is the spec the agreed on notation?  If so, I'll change the paper.

I think  that works for any "autozygotic" object.   Otherwise I think it needs to be something like "singleton(e)" 
this is related to pattern matching, because types are patterns.  Michael? 

James