Enhancement: Add Markdown Export Support

[hasansezertasan]

Thanks for the great job 🙏.

It would be very helpful if there was an option to export as Markdown 🤓. I would be happy to help if it's OK 😇.

[dragonish]

The functionality should be easily achievable. However, for other attributes in the bookmark, such as creation date and icons, what would be the best format to represent them in the final .md file?