Upsampling support

[pattonw]

I was about to try implementing a lazy downsampling of a dask array, but the downscale_dask looks perfect for my usecase. I also need to lazily upsample a dask array. Would that be a useful addition to this library or should I keep that separate? I was thinking I would just need to implement upscale_dask, upscale_coords, and upsampling_height and add them to the multiscale module.

[d-v-b]

yeah that sounds like a nice addition!