These go into the architecture/block of their scope and will be
used by component instantiations to make sure the bindings are
correct and complete.
Also handle signal declarations. The elaborator will use these
to generate module local variables that are used by the architecture.
Elaboration will need a parse tree for expressions. Create one for
the expression types that are currently supported. Also add rules
and the keywords for all the remaining binary logical operators.
Stephen Williams