Add examples that demonstrate limitations of the current elaborator. The new design, we are working on, will be able to solve them.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add light_checker: module for extracting the type of (fully elaborated) expressions. It is much faster than type_checker, which infers the type but also check whether the input is type correct or not.

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