Create a symbolic link pointing to src named dst.
target_is_directory is required on Windows if the target is to be
interpreted as a directory. (On Windows, symlink requires Windows 6.0
or greater, and raises a NotImplementedError otherwise.)
target_is_directory is ignored on non-Windows platforms.
If dir_fd is not None, it should be a file descriptor open to
a directory, and path should be relative; path will then be relative
to that directory.
dir_fd may not be implemented on your platform. If it is unavailable,
using it will raise a NotImplementedError.