Update build script and docs config to handle newer versions

[evertrol]

Newer versions of Python, Jupyter-nbconvert and Sphinx can now work with the build system, using a few simple workarounds.

[evertrol]

I'm aware of the discussion in #47 . It's mostly that while searching for ODE examples with SciPy, I came across this cookbook. I can see it's definitely outdated, but it still had some use for me, and I've tried to update the ODE examples (see pr #59 ) with minimal changes.

If there is still interest in revitalizing this cookbook (perhaps as discussed with omission of various topics), I might attempt to update other notebooks as well. Updates so far mostly have been largely stylistic, and consist of applying more of a notebook style with code spread across multiple cells instead of being a single script, and using either newer APIs (pyplot instead of pylab mostly, and solve_ivp instead of odeint for the ODEs) or fixing arguments in older-style APIs.

To test and build the cookbook myself, I had to fix a few issues in the build script, which is why this PR exists.

[j-bowhay]

Thanks @evertrol apologies for the wait!