Consider migrating away from Vista/Windows2003/Windows7 namespaces

[machish]

Now that Windows 7 is no longer getting Security Updates, and there are many different versions of Windows 10, it may make sense to take steps to get rid of the Vista/Windows2003/Windows7 namespaces.

• Copy all of the grbits/APIs from Vista/Windows2003/Windows7 to the main namespace, helping with discoverability.
• Remove many of the compatibility tests.
• In a future release, remove the Windows2003/Vista/Windows7 namespaces. Obviously that would be a breaking change, so could be done later (or not at all?).
• Leave Windows8/Windows81 alone for now, since they are still supported OS's.