Vavr: Add leftPadTo(int, T)

[danieldietrich]

We already have Seq<T> padTo(int, T).
Now we want to add Seq<T> leftPadTo(int, T) in a similar way.

Motivated by this article.

[mvh77]

Meaning Javaslang won't be found on NPM after all? :stuck_out_tongue_winking_eye:

[danieldietrich]

Successfully finished.