pathlib.Path.glob does not follow symlinks

[Keunmo]

It is same issue as introduced in cpython.

Shortly, if there are symlinks under Path(root), Path(root).glob('**/*') does not catch all pathnames from symlink.

So it makes error if user use symlink at datasets and do extract_features.py

Solution is simple. Just replace Path(root).glob('**/'+g) with Path(root).rglob('*/'+g).

I'll open pull request for this issue soon.