customCSS url() rewriting is broken on Windows

[rjgotten]

URLs in customCSS that are rewritten, end up broken on Windows. The rewriting logic uses the path module, which uses \ as the separator on Windows and you end up with broken URLs.

[jgerigmeyer]

Thanks! A PR (with tests) would be welcome; otherwise I'll try to get to this in the next week.

[jgerigmeyer]

@rjgotten We're now running tests against a Windows environment, but I don't have a good way to functionally check that this is working in Windows. Would you be willing to try against the master branch and see if this is adequately fixed? Thanks!

[rjgotten]

@jgerigmeyer
This seems to be working OK now.
The paths are correctly rewritten.

When installing the master branch directly via npm install I have a bit of a problem though; seems the entire /assets/webpack folder is gone. So I cannot actually test the entire documentation in vivo.

Have to go off of what I can read when I open the custom css file in /assets/custom in my text editor.