Higher order nonuniform interpolation

Hi,

I'm using Interpolations.jl over in [MethodOfLines.jl](https://github.com/SciML/MethodOfLines.jl), and am finding it very convenient for providing an interpolating interface to the solutions of PDES there. The solutions that it produces are most often nonuniform in at least the time dimension, and I would really like to be able to provide higher order interpolations for these solutions.

What would it take to implement higher than linear order nonuniform interpolations, for example a B-Spline interpolation? I'd be happy to implement this feature, if you could point me in the right direction.