Relative image links in pages below the top-level document folder seem to point to the wrong path.
Reproduction
I've created a minimal reproduction case:
https://github.com/jdhoek/mkdocs-test-relative-image-links
The reproduction case contains this file structure:
├── docs
│ ├── index.md
│ ├── subdir
│ │ ├── sub.md
│ │ └── sub.png
│ └── toplevel.png
└── mkdocs.yml
mkdocs serve and mkdocs build correctly process the Markdown files in the top-level folder docs_dir, but with the Markdown file in the sub-folder the relative image links are broken.
