fix(library/elaborator): hack for fixing a bug due to pairs/projs, this is temporary fix until we build a new elaborator

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(builtin): define list, cons, nil and prove basic theorems

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(builtin): define list, cons, nil and prove basic theorems