Images being written to `source/`

[trevorcampbell]

In Chapter 5, I saw an image being written to the source folder

plot(fig, filename="img/classification1/fig05-more.html", auto_open=False)

We should go through the whole book and ensure that all output is only being written to _build/

[trevorcampbell]

I see now why things were set up this way...saving to _build does not seem to work.

It's not great though. We should revisit later. This is not super high priority for now.

[trevorcampbell]

After #240 , the 3d viz are no longer saved to disk. So this might be stale now. Needs investigation

[trevorcampbell]

Confirmed that this is no longer happening. Closing