Mechanism to slice variables

[ayan-usgs]

The sgrid standard specifies a padding parameter on coordinates defined within in the staggered grid. Depending on what is being done with a variable, it may be necessary to use the padding to trim rows/columns off a dataset. The pysgrid sgrid creates a slicing attribute (e.g. center_slicing) on variables to help with this, but the use it the slicing attribute typically requires it to be sliced. The package should be able to infer how to slice the variable from the dimensions and coordinate names, rather than relying on user input.