[Grace-core] Binding symbol and egality symbol

[James Noble]

> Incidentally, I also agree with the choice of "const" as a keyword.  
> When I saw the "let" I immediately wondered why that was chosen.  
> "const" is immediately clear and expressive, "let" requires  
> explanation and interpretation.

I don't think there is a good solution here - at least not in English.  
The problem with "const" - or scala's "val"
is that, well, the object being bound to the name isn't necessarily  
constant (or a value)
const at least has the associations from Pascal.

I'd originally hoped to follow Self - without any keywords, which is  
why the symbols were different.

fixedSlot = anObject

variableSlot <- anObject

Hmm: perhaps "fixed"?

James