[Grace-core] Information hiding

[James Noble]

> Coming up with a semantics for this is very tricky.  I'm not convinced that it is necessary for a teaching language, since we can information hiding quite adequately  by convention.

well yes, but if there's a convention, then we should check it
 thinking back to the _private convention from Dart,
or the   Public/private conventions from dotNet and Go

> Addressing this properly requires encapsulation policies; I don't believe that we can do those with annotations, since they require a run-time representation.

right.  -- well, some like the above to may be doable dynamically by leveraging the names we've already got -- but especially if we want protection on a per-package basis, then
we'll need runtime representation of the *packages*.

And if each package is an object (newspeak style) perhaps the per object protections
generalise to per-package -- that's what I'd kind of hope --- but I'm not sure how much
it really does what we want

Jame