Add rechunk function

[felixcremer]

This adds a rechunk function which would return a RechunkedDiskArray
This function could then be overloaded by wrapping packages like DimensionalData.

This was discussed in #35 but is not a fix to that but would open up a better workaround.
This would need some tests

[asinghvi17]

Would it make sense to allow any sensible definition of chunks here? I think rechunkeddiskarray takes tuples of chunksize like (10, 10, 3) for instance...

[asinghvi17]

rechunk(data::AbstractDiskArray, chunks::GridChunks) = RechunkedDiskArray(data, chunks)

just for style

[meggart]

I start wondering if rechunk might be a misleading function name. In the end, we are not rechunking the data but rather creating a view into the data that behaves as if it was chunked in a different way internally. There might be some confusion among users when they assume that the result of rechunk would magically make time series access more efficient on spatially chunked data, this happens quite reularly in the python world for xarray's chunk function.

I think we need either a different name or at least a better docstring explaining that no physical rechunking is happening here.

[felixcremer]

Yes, i am also wondering whether the name setchunks makes more sense. I could copy the docstring from the YAXArrays.setchunks function and remove the YAXArray specifics.

help?> YAXArrays.setchunks
  setchunks(c::YAXArray,chunks)

  Resets the chunks of a YAXArray and returns a new YAXArray. Note that this will not change the chunking of the underlying data itself, it will just make the data
  "look" like it had a different chunking. If you need a persistent on-disk representation of this chunking, use savecube on the resulting array. The chunks argument can
  take one of the following forms:

    •  a DiskArrays.GridChunks object

    •  a tuple specifying the chunk size along each dimension

    •  an AbstractDict or NamedTuple mapping one or more axis names to chunk sizes

[rafaqz]

Even setchunks seems more active than it is... It's really like fakechunks

[felixcremer]

Fakechunks sounds like it is not chunked at all. But I see your point.
Other possible names could be:

pretendchunk
pseudochunk
mockchunk

And if we rename the function we should also rename the main object because it would be good to have them in accordance.