Convert external links to internal note references
This is a slightly more complex function that is for conversion of external reference links into internal note reference links.
For example, imagine you have have used hexo to write blogs using absolute paths to reference other notes or posts. Having migrated to Joplin you might now want to convert those absolute paths to internal Joplin references so as to avoid the "404 problem" caused by a change in the URL of a given post. This function was created to simplify this operation.