Clarify that reveal.js 3.x is needed

[takluyver]

Closes gh-702

[damianavila]

+1 as I said in the issue.

[mpacer]

Looks good but I still think that the default of using the cdn (#732) is a better default for most people… unless we want to explicitly help people download an up-to-date version of reveal.js. My intuition is that we should provide that utility with something like a --standalone flag that downloads the version of reveal that we get from the cdn at runtime (or something that checks if it’s already present and only downloads it if it’s not present). Lots of people who are capable of using the CLI but aren’t familiar with js will run into issues around this otherwise (e.g., it’s unusual to have a directory with a js extension if you haven’t seen it before; that’s not the only reason but it’s emblematic).

[mpacer]

Actually can you add a reference to the latest example of reveal.js that works? Also a test to make sure that the version mentioned in the docs works? That way, we’ll know if it ever breaks with the a nbconvert change?

[takluyver]

I've added a note to the docs showing how to get reveal 3.6. Adding a test that reveal.js works would be a big job, however - it involves executing Javascript in a browser, which the nbconvert tests are not set up to do. And we know from the notebook tests what a pain it is.

[damianavila]

We are using reveal.js 3.5.0 in the serve post-processor, we should keep it consistent and checkout 3.5.0 until we decide to upgrade the whole thing to 3.6.0, I think.

[takluyver]

Thanks Damian, updated.

[mpacer]

Closing since we now have #732 merged with this inside of it.