Add Tests

[reuseman]

The next goal in the rewrite is to figure out how to test the plugin. A simple idea could be to have a list of markdown files that will be parsed by the plugin. But maybe something better can be done, to involve in the testing phase the interaction with the Obsidian APIs. Resource to look at
https://publish.obsidian.md/hub/04+-+Guides%2C+Workflows%2C+%26+Courses/Guides/How+to+test+plugin+code+that+uses+Obsidian+APIs

Moreover, the markdown files should be written based on the previous closed issues and the current ones.