[functions] Migrate exercise to use sphinx-exercise

[shlff]

Hi @mmcky , this PR converts exercises and solutions of lecture functions using sphinx-exercise's syntax.

I noticed two weird things in the following preview:

• for Exercise part, the name for exercises are Exercise 4.1, Exercise 4.2, Exercise 4.3, instead of Exercise 1, Exercise 2, Exercise 3.
• for Solution part, it fails to execute all python cells!

For the issue in exercise numbering, I tried to use nonumber option. It just shuts down the whole numbering for exercises, but I don't find a way to change the names of exercises.

[mmcky]

We are doing a major refactor of sphinx-exercise so once that is done we can use this as a test case.

[mmcky]

@jstac I think we could enable sphinx-exercise for the lectures more generally now that latex is supported.

While code-cell isn't directly enabled what do you think about this approach for the interim:

https://617656cde2d4e2288538c01a--epic-agnesi-957267.netlify.app/functions.html#solutions

I think it looks OK with code-cells following the solution block (so that it executes).

[jstac]

I think it's very sensible :-)

I wonder how we can get this done though. We are short on RA money. Any thoughts?

Do we have Sloan money we can spend?

[mmcky]

@jstac there is a great case in writing_good_code that shows we really need the gated directives (ideally). It has a lot of code-cell directives mixed in with text and hard to make it look cohesive in the above approach.

We could either:

• migrate the lectures that contain straight forward cases as this is the majority of cases
• put this on hold until we have gated directives (~1-2 months)

[mmcky]

Closing in favour of #176