Simplify enchantment ranges

Minimums can be calculated using `min = ((power - 1) * minInc) + minVal` where `minVal` is the minimum value for power 1, `minInc` is `minAt(2) - minAt(1)` with respect to power, and `power` being the level of the enchantment (1-5).

Maximums can simply be calculated as `max = min + offset` where `offset` is the constant difference between the maximum and minimum for any given power / level.