feat(library/standard/data/option): add basic theorems for option types

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(library/standard/logic/class/decidable): add missing 'end'

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(library/standard/logic/class/decidable): add missing 'end'