Plotextractor

- Try to preserve the ordering of figures.

- Handle utf-8 in paths inside the tarball.

- Ignore hidden/metadata files in the tarball.
- Handle relative paths in the tarball.

- Sets the mtime for all members of the tarball to current time before
unpacking.

- Properly raises an exception when no TeX files are found in an archive.
- More fixes to image path extraction and more robust image handling.

- Fixes linking images from TeX reference when images are referred
to without specifying full relative folder path.