Consider fastpages instead of jupyter-book

[MaxGhenis]

The jupyter-book lead developer mentioned in an issue that:

I think we have to walk a balance between re-creating all of the features of a blogging platform (since that's not technically in-scope of Jupyter Book) if it adds a lot of maintenance burden

I'm also concerned about how often jupyter-book requires rebuilding, at least when testing so far. This won't be sustainable with many blog posts.

This prompted me to look for alternatives that are geared more at blogging, but still with jupyter-book features like hiding/showing code, Jupyter input, interactive visualizations, etc. I found http://fastpages.fast.ai, which looks like a pretty great option. The only potentially missing feature is plotly support, and it also worries me a bit that there isn't much in the https://github.com/fastai/fastpages repo. But worth trying out I think.