feat(library/standard/bool): add band_assoc and bor_assoc theorems

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/standard/bool): add bor_to_or theorem

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/standard): add basic set theory that does not rely on classical axioms

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