Fixed segfault in CParser __reduce__ method
Disabled multiprocessing for Windows tests
Warn when parallel feature is enabled on Windows
Changed windows exception to an error and made tests xfail
Fixed minor problems with parallel keyword
Speed up Column slice setting by defining a __setitem__
Add comment to __setitem__ about why it exists.  [skip ci]
Change spherical<->cartesian conversions to a representation-based implementation

Moved them to a new module in the process
Fix a minor issue I discovered with class-deprecation.  In short, the new class's __init__ should receive the same treatment __getstate__ and __setstate__ (unfortunately the same really goes for any method that might use super(), which is not addressed here.  But this should be fine for most important cases.
Changelog entry
Alternate fix that works by eschewing subclassing the original class, and instead just tossing it away outright and building a new class.  There are still some obscure cases where this won't work, especially in the case of custom metaclasses.  But those cases can be dealt with if really needed...
Merge pull request #3004 from embray/utils/fix-deprecated-class-super

Fix deprecated decorator on classes that use super(...).__init__
Fix problem with hstack and duplicate input tables
Merge pull request #2995 from taldcroft/table-hstack-2995

hstack fails with duplicate column names
Merge pull request #3003 from eteq/move-sphercart-to-convenience

Change spherical<->cartesian conversions to a representation-based implementation
Merge pull request #2994 from mhvk/column-setitem-speedup

Improve performance of table column setting
Merge pull request #2969 from amras1/disable-multiprocessing-windows

Disable io.ascii multiprocessing on Windows for now
allow WCS slices with slice(None,None,X) and slice(None,x,y)
fix test: *2, not /2
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