Minimize features

[Philippe-Cholet]

Somehow, I looked at try_collect and ticked seeing that it needs use_alloc. It sure does in most common cases but we can collect to arrayvec for example.
Because of that, I looked at each adaptor/method to find another unrequired features and found only the ones based on extrema_set which only needs to allocate to vectors.

[Philippe-Cholet]

@jswrenn This seems straightforward to me. What do you think?
I guess I'm reserved about expanding try_collect usage (to "no std") because of the nightly version in core.
But I don't see any problem about the "extrema_set" methods.

[jswrenn]

This looks good to me!