[import] Add reference count handling (when finding internal links + mapping to pages)
This issue is a todo.txt import (see #5 (closed)). Its priority is unknown.
The use case was to find orphaned and missing pages:
- Count/handle orphaned pages (present, not referenced)
- Count/handle missing pages (not present, referenced)
As in #9 this would require indexing of all pages on startup and keeping the reference count up-to-date with changes on the file system. Since this is a nice-to-have feature, it does not influence of the priority if the indexing implementation. But it should be prioritized if the index implementation is progressing to include it in the use scope of the indexing implementation.