The 'windows' directory is mainly useful for
maintainers, not end users. So I moved it out of
the root to reduce distraction for a first-time
visitor.
While I was fixing up resulting breakage in
Visual Studio project files, I noticed I still had
some hard-coded absolute paths that would only work
on my own Windows laptop (e.g. "c:\don\github\astronomy").
I replaced those with relative paths that will work
regardless of what directory the repo is cloned into.
