@Nonnull
    static VariableAmount baseWithVariance(double base, @Nonnull VariableAmount variance) {
        return new BaseAndVariance(base, variance);
    }
Creates a new variable about which has a base and variance. The final
amount will be the base amount plus or minus a random amount between zero
(inclusive) and the variance (exclusive).

@param base The base value
@param variance The variance
@return A variable amount representation
helper/src/main/java/me/lucko/helper/random/VariableAmount.java