Parameterized ability stacking rules

**What do you want to see?**
Ability stacking rules that take parameters. For instance, an exponential rule that stacks things but the best item is at 100%, then 50%, then 25%, using an exponent of 0.5. Or a Pythagorean rule that uses the Pythagorean formula in a specified number of dimensions (e.g. Stars! used a 4-dimensional Pythagorean formula to give sensors diminishing returns).

**How would it help players?**
Things could stack that didn't before, without being insanely OP, if we add these kinds of rules. Plus whatever crazy stuff modders think of!

**Alternatives**
We could hardcode some values, but parameters are more fun! Also, perhaps these values could actually be formulas that somehow take a list of values and output a single value?