2.x: Design.md +extension +fusion (#3980)
2.x: Design.md +extension +fusion (#3980)

* 2.x: Design.md +extension +fusion

* Flatten the create-table

* Update create naming to avoid overload conflicts

* Add missing explanation, remove words

reactivex/rxjava,NiteshKant/RxJava,akarnokd/RxJava,benjchristensen/RxJava,AttwellBrian/RxJava,artem-zinnatullin/RxJava,reactivex/rxjava,artem-zinnatullin/RxJava,akarnokd/RxJava,ReactiveX/RxJava,NiteshKant/RxJava,AttwellBrian/RxJava,ReactiveX/RxJava