make it work on WINNT with '/reference' on WSL

[refack]

Three parts:

1. demangle filenames re.sub(r'[\uf000-\uf0ff]', lambda m: chr(ord(m.group(0)) & 0xff), filename).
   Apperently WSL1's drvfs will turn incompatible ASCII characters in filenames (* : ? |) into unicode \u0xf0XX.
   For maximal tarball name preservation I exploded it to a WSL1 path, but read it from native windows, so we need to demangle before processing, but keep mangled name for renaming, so we map both to the new name
2. replace uses of os.path with import posixpath as urlpath for most URL path manipulations
3. Use pathlib.Path when constructing URLs to the live website.

If there's interest (or if it makes my workflow simpler) I'll figure out how to handle a tarball exploded in native WIN32.