Is there any advantage to keeping the old interface, or should this eventually replace Rbf entirely?
My intention is for `RBFInterpolator` to replace `Rbf` entirely. It should be possible to replicate the functionality of `Rbf` with `RBFInterpolator` (albeit with warnings when the interpolant may not be well-posed). `Rbf` is not currently deprecated in my PR, but I can make that change if you think it is appropriate.
-Trever