docs: obsidian compatible

[philiplinden]

There is a lot of tedium writing notes in my text editor, so I decided to open the whole repo in Obsidian and see how it goes.

The changes here aren't strictly necessary but I find it makes it easier to bridge the gap between how i want the docs to look when published and how I want to work with the files locally, but without adding too much file bloat to the repo.

Obsidian fits this quite well because it works with markdown files natively, has a lot of convenience features like backlinks and auto-updating links, and front-matter for advanced organization. mdBook is super lightweight in the repo and I don't need to add tons of web related files to the repo to make a pretty site for it (unlike many obsidian site generators). I find this to be a happy medium.

• Moves the publishable book files into src to separate them from dev docs
• Adds dev folder to hold other notes that I don't intend to be published on the site but are still relevant to the project
• Moves devlogs into dev/log with separate files for each day
• Removes devlogs from the published site
• Adds mdbook-yml-header plugin to hide yaml frontmatter from notes (if it exists) - this is to clean up any front matter Obsidian might add when working with the notes so it doesn't clutter the rendering but I can still make use of that front matter.