[Draft] Migrate to value classes and specialized generics

[Glavo]

After JEP 218 and JEP 401 are delivered, we should migrate to value classes and specialized generics. To achieve this, we need to redesign a lot of APIs. Before that, kala-common will not be officially released.

This Issue is used to record the refactoring that needs to be done in the future.

• Delete all AnyXxx classes/interfaces, PrimitiveXxx should directly inherit Xxx.
• Delete all xxxOrNull methods, because xxxOption no longer has the boxing overhead.