Add support for all note attributes

[alexander-tobias-bockstaller]

The ENEX DTD defines a lot more note-attributes than those that are currently supported by yarle:

• subject-date
• latitude *
• longitude *
• altitude
• author
• source
• source-url *
• source-application
• reminder-order *
• reminder-time*
• reminder-done-time *
• place-name
• content-class
• application-data

Only those starred with an asterisk (*) are currently supported. I found that at least author and source are used in my personal notes and wanted to preserve these when migrating to Obsidian.

I therefore decided to clone the repo and make my first ever github contribution. However, I'm not a TypeScript guy, so I'm really not sure if all my changes are ok. Also, I'd love to trigger some of the Test workflows before creating the PR, but looks like I need permission. As I said, this is my first ever github contribution, so let me know if I missed something or if what I'm doing is not the way it should be.

Cheers.