Interpolation convenience methods for higher dimensional data

[cnrrobertson]

It would be helpful to have methods for interpolating an n-dimensional array along a given axis as was discussed in #67 (comment).

This is currently possible just by "vectorizing" data along that dimension. Example:

data_3d = collect(reshape(1:125,5,5,5))
time = 1:5
vectorized_data = collect.(eachslice(data_3d,dims=3))
spline = CubicSpline(vectorized_data, t)

Is there an interest in having these conveniences or should that be left to the user?