泛型 x 多載的侷限紙條

比如說:

Completable RxTask.from(Task<Void>) {}
Single<T> RxTask.from(Task<!Void && !Iterable>) {}
Observable<T> RxTask.from(Task<Iterable>) {}
Task<Void> -> Completable
Task<!Void && !Iterable> -> Single
Task<Iterable> -> Observable