errors: Store and show traceback information from Monte code.

Backport of a similar feature from the future times.

Signed-off-by: Corbin Simpson <cds@corbinsimpson.com> <simpsoco@google.com>
objects: Start splitting out objects, beginning with constants.

Comes with a full suite of tests for null, true, and false.

This patch is painfully large, but there's no way around that; typhon.objects
had this coming for a while and it had to get broken up sooner or later. Might
as well do it now!

Signed-off-by: Corbin Simpson <cds@corbinsimpson.com> <simpsoco@google.com>