Interpolation

[aplavin]

Currently, there's no convenient interpolation integration for AxisKeys, as far as I know. The readme says

There is no interaction with interpolation, although this seems a natural fit. Why doesn't A(:left, 13.7, :) interpolate along continuous dimensions?

I think it's best to keep basic lookup like A(:left, 13.7, :) to only retrieve existing values, as it currently does.
But something more explicit could be very convenient and composable: maybe, A(:left, Interp(13.7), :)? This generalizes to A(:left, Interp(13.7, order=2), :), for example.

Such an interface looks general and intuitive. Do you think it would make sense, or there are better alternatives?