Option to squeeze singleton dimensions

[bekozi]

Add option to squeeze singleton dimensions following a slice. This could also apply to processing data with a singleton dimension in general. Right now, the singleton dimension is left in to maintain the source value and/or original data shape.

One possible approach:

ops = ocgis.OcgOperations(..., squeeze_options={'slicing': True, 'as_dimensionless': True, 'reshape': False})

Documentation:

• slicing :: If True, squeeze singleton dimension following a slice.
• as_dimensionless :: If True and the dimension has an associated coordinate variable, convert the coordinate variable to a dimensionless, single-valued variable. Otherwise, leave the coordinate variable as is.
• reshape :: If True, squeeze variable dimensions if they are singleton respecting as_dimensionless.

Ping @nkadygrov.