Fix bug in normalizer. We must create a scope whenever we extend the value stack.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add support for metavariables in the normalizer.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Simplify metavariable context. Now, we have only 'lift' and 'inst' instead of 'subst', 'lift' and 'lower'

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Cleanup meta_entry code

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>