Windows testing: attrib +h (hidden files), mklink (symlink equivalent?), file.mode

[webketje]

Need to do some local tests on a Windows machine to see how it behaves with:

• files hidden with attrib +h, see https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/attrib
• mklink, see https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/mklink . If this works some tests now skipping Windows could be run there too
• Metalsmith.File.mode: need to do some testing, it looks like this does support perm sets 444 & 666 for Windows, see https://github.com/nodejs/node-v0.x-archive/issues/4812