Flatten namespace

[mrocklin]

I think that in order to use the imread function I need to dive within the imread module today

import dask_image.imread

x = dask_image.imread.imread('...')

This might be more user friendly if it was just

import dask_image

x = dask_image.imread('...')

Separately, it also looks like this is the only function in the imread module. I wonder if maybe having a seaprate module here is overkill for now?

[mrocklin]

It looks like scikit-image uses an io module?

[jakirkham]

Sure this is mostly inherited from the old dask-image org layout. Moving to an io module seems reasonable.