Added the alternate push pull function

[NandoBongers]

No description provided.

[mgottschlag]

I believe this is wrong - the function does what the existing function into_alternate() is supposed to do. However, maybe I am overlooking something.

In any case, the modification to OTYPER has to be present in into_alternate() as well, because that function must not produce a open-drain pin if the same pin was previously used with into_alternate_open_drain().

If I am overlooking something, please explain what you had in mind with this PR. :)

EDIT: What I want to say is that your new function should be renamed into_alternate() and the old into_alternate() should be removed, essentially.

[NandoBongers]

Hello @mgottschlag I renamed the functions as you suggested in my latest commit.

[luctius]

I see no further issues with this commit.

Edit: could you run a cargo clippy & cargo fmt