Passing a buffer to `extrapolate`?

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
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.

Start by locating the `extrapolate` entry point and the `neville` tableau implementation, then reproduce the reported allocation benchmark. The work is done when `extrapolate` accepts a sufficiently sized buffer for the tableau diagonal and the benchmark demonstrates that the buffer avoids the reported allocations.

Written by the indexing model from the issue text.