argmin/argmax functions for Vec*

[EmbersArc]

I recently had to get the index of the maximum element in a vector and noticed that argmax does not exist. Maybe adding that and argmin would make sense as the functions are somewhat common. I can open a PR should we decide to add it.

[bitshifter]

I have needed to do that occasionally as well, so that does seem like a useful addition.

I haven't come across the argmin / argmax naming before, I see that's common in science and mathematics communities, I wonder if there's a more discoverable name that could be used for people who aren't familiar with argmin/argmax and wouldn't think to look for it. Maybe something like max_position or position_max on the basis that this would be similar in function to https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.position. max_position would show in in IDEs when users start typing .max.

Happy to look at a PR for this.

[EmbersArc]

Thanks for the response! With e.g. #[doc(alias = "argmin")] we can make the functions discoverable to those looking for the mathematical term. I opened #615.

[bitshifter]

Added in #615