Tuning类是否应改为抽象类？/Should the class Tuning be an abstract class?

[zhenlige]

目前Tuning类的实例化只用于纯律及其拉伸，这一功能也可以由质数映射为空的PrimeMapTuning实例实现，但不确定是否会造成严重的性能开销。

Currently the instantiaton of class Tuning is only used for JI and is stretched version, which can also be achieved by an instance of PrimeMapTuning with an empty prime map, but it is not sure whether this will cause severe loss of performance.