[Feature] make create_region_mesh support normal keyword arguments

[PolarBean]

At the moment create_region_mesh takes a tuple as an argument. This is for compatibility with multiprocessing libraries. I would suggest using more standard function arguments and having a wrapper function which accepts the tuple. I have implemented this as part of this PR
#727 and opened this issue so we can discuss just the mesh function aspect.

[adamltyson]

Sounds sensible to me. I think @IgorTatarnikov was the last one to look at the mesh generation, so he will have a better idea of how to proceed.

[IgorTatarnikov]

I have no problem with the new approach (the functions should be renamed (i.e. create_region_mesh and create_region_mesh_wrapper).

If I understand the problem though, we could upstream this decision a bit. The check for skipping could be done here, this way we only queue work that will actually create a mesh. This way create_region_mesh doesn't need to know whether some ids need to be skipped.

This might even result in a slight speed up, inter-process communication has a penalty so we should avoid sending work that returns immediately.