Static assets

[avivace]

There should be a way to set a folder to be served as static, without having to put assets in the book folder

[joshrotenberg]

The serve option is mainly for testing while you work on your book, so while you could potentially add this functionality if the assets aren't part of the built book directory they'd be orphaned in any other situation unless your other hosting situation (i.e. GitHub Pages) was also able to reference the static assets elsewhere.