fix: _stat_mode can follow symlinks pointing to a relative path

[khsrali]

_stat_mode couldn't follow symlinks that are pointing to relative paths. As a result, _stat_mode of the symlink was returned instead of the target.

This PR adds an extra check if the target path of a symlink is a relative path; it resolves it.

In addition, a new function relpath is added for the sake of completeness. This will prevent users to manually transforming each FcPath to Path in order to get the relative path.

[ekouts]

Thanks a lot for the contributions @khsrali ! I was going to approve, but just noticed that the type check fails, would you have time to take a look to that? :)

The truth is I haven't been maintaining very well FcPath even though it is probably interesting to other users as well! No need to do it in this PR, but if it some point you would have some time to add some documentation in rtd it could help me and others :)

[khsrali]

Hi @ekouts ,
Thanks, I'll fix it by tomorrow the latest.

The truth is I haven't been maintaining very well FcPath even though it is probably interesting to other users as well! No need to do it in this PR, but if it some point you would have some time to add some documentation in rtd it could help me and others :)

Absolutely, you are right, it's good to have some documentation. Will do in a separate PR :)

[ekouts]

Great, thanks!