Foliantcontrib.superlinks

- Anchors added to beginning of files are not random anymore.

- Fix imports.

- New utils module.

- Fix: BOF anchors bug
- Fix: common paths processing

- Fix: proper relative path generation for links.
- Fix: multiple issues when !path modifier is used in the link tag.
- BOF anchors now won't be added for mkdocs backend.

- If tag body it empty, superlinks will try to guess the right caption of the link:
- referenced title for links by title,
- meta section title for links by meta section,
- heading title for links by CustomIDs,
- title from config or first heading title in the file for links to file,
- anchor name for links by anchors.