Commit 2018-05-27 18:15 ad92a9ba

feat(algebra/group,...): add with_zero, with_one structures other ways to add an element to an algebraic structure:

• Add a top or bottom to an order (with_top, with_bot)
• add a unit to a semigroup (with_zero, with_one)
• add a zero to a multiplicative semigroup (with_zero)
• add an infinite element to an additive semigroup (with_top)