Support xPath for Windows pathnames

[albertvillanova]

This PR implements a string representation of xPath, which is valid for local paths (also windows) and remote URLs.

Additionally, some os.path methods are fixed for remote URLs on Windows machines.

Now, on Windows machines:

In [2]: str(xPath("C:\\dir\\file.txt"))
Out[2]: 'C:\\dir\\file.txt'
In [3]: str(xPath("http://domain.com/file.txt"))
Out[3]: 'http://domain.com/file.txt'

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[lhoestq]

Cool thanks ! Maybe just one test:

[lhoestq]

Thanks ! :D