[Grace-core] Edited Variable & Constant page

[James Noble]

> I would NOT like to use := to initialize constant bindings.  I can  
> go either way with initializing variable fields, though probably  
> prefer :=, as it makes it parallel to regular assignments.

yep, me too here. I also like the way the terms of discussion are  
playing out
"constant bindings" vs "variable fields".

I did wonder if "ref" was a shorter alternative to "const"
(or even "def" but that would be perverse compared to Scala)

J