When annotations (highlights and notes) are exported to the markdown format from books with complex multi-level TOC such as:
```
- Chapter 1
- 1.1 sub-chapter
- 1.1.1 sub-sub-chapter …
Hi,
I have built `protoc-gen-doc` from source on OSX (10.11.6) (from master, commit 97718abd9571d9e71651478f160d11dfefba543c) following the given steps. HTML output seems correct but markdown output …