Windows Visual Studio Project needs updating

[nigels-com]

I had a go today building GLUI on Windows 10 with Visual Studio 2019.

Some issues I came across:

• Visual Studio insists on "migrating" the projects to the current version, which isn't an ideal experience.
• The linker flag combination is not supported, needs to be manually fixed.
• Some source files have been renamed, needs to be manually fixed.
• The projects don't who how to include GLUT headers or link the library.

Options:

• Remove the projects, recommend cmake instead.
• Leave them as-is in case someone wants to rehabilitate them.
• Update the projects for Visual Studio 2019, or an earlier version that plays nicely with the current one.

[nigels-com]

The other issue I bumped into is including windows.h with the NOMINMAX macro, which GLUI isn't doing systematically. Suggests to me that Windows support has been broken for quite some time. I'm not sure if current Visual Studio is still defaulting to Win32 mode. (WIN32? _WIN32?)