Stack class name

[dfirestone21]

https://www.raywenderlich.com/books/data-structures-algorithms-in-kotlin/v1.0/chapters/4-stack-data-structures

When creating the StackImpl class you name it Stack, which is the same name as the Stack interface. You then refer to it as StackImpl for the rest of the chapter.

Also there’s quite a few grammar errors in this chapter and it can get distracting.