Passing a buffer to `extrapolate`?

[maltezfaria]

I have some code that makes constant use of extrapolate, and while probably not a bottleneck in my use case, I was wondering if it would be possible/desirable to modify extrapolate so that we can pass the buffer used to store the diagonal of the neville tableau. Here is what I get right now:

julia> @btime extrapolate(cos, 1)
  73.269 ns (3 allocations: 160 bytes)
(1.0, 1.4518386493023172e-12)

The goal would be to allow e.g. extrapolate(cos,1;buffer=...) to avoid allocations provided buffer is an empty vector of sufficiently large capacity.

I would be happy to put together a PR if this seems desirable.

[stevengj]

A buffer keyword argument seems reasonable here.

(The extrapolate! function is allocation-free, but requires you to decide the evaluation points in advance.)