Add rollaxis and moveaxis

Would be nice to have Dask Array implementations of rollaxis and moveaxis. This can probably be done relatively easily by building off of transpose.

[shoyer]

I’m just wondering do the docs spell this out somewhere? Ideally the API description would say this, but I’m not seeing it. Am thinking about this from the perspective of a C/C++ programmer where the docs really are the gold standard about what the library does.

Agreed, see https://github.com/numpy/numpy/issues/9476.

[shoyer]

These functions already work on dask arrays, since they are defined in terms of the transpose method:

In [1]: import numpy as np

In [2]: import dask.array as da

In [3]: x = da.ones((10, 11, 12), chunks=7)

In [4]: np.rollaxis(x, 0, -1)
Out[4]: dask.array<transpose, shape=(11, 10, 12), dtype=float64, chunksize=(7, 7, 7)>

In [5]: np.moveaxis(x, 0, -1)
Out[5]: dask.array<transpose, shape=(11, 12, 10), dtype=float64, chunksize=(7, 7, 7)>

So we could probably just add appropriate aliases here.