Fix broken links to pages with the same name as title

[lukasrynt]

Hi @daxcore, I adopted your plugin for one of my personal projects and find it really great. However, I found that if the project's name is included in one of the links it would not create the graph properly. Consider the following scenario:

• Example page/docs/Example
• Example page/index

In your implementation, for the link Example, the regex would capture both of the above expressions and would later choose the index page rather than the correct Example page, since it's shorter.

This MR fixes the issue by adjusting the regex to match against nodes, that are at the end of the path and also adds tests that show the issue. I also made some slight refactors to parts of the plugin.