refactor(library/logic/connectives/eq): simplify eq_rec_on_id proof

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/logic/connectives/basic): add not_not_em theorem

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(frontends/lean/info_manager): store environment+options in the info_manager, fixes #96

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