Fix epub library issues.

[voidberg]

Currently, there are some issues with the epub library we use:

• A ToC is forced. See if we can skip it.
• Add better error handling since some articles are never generated due to errors.

Alternatively, see if we can create a simpler version of the library. Even better, see if we can output KEPUBs directly so we don't rely on kepubify.

[voidberg]

Decided to implement a simple ePub library: voidberg/quarto