Add approaches for sum-of-multiples exercise

[clechasseur]

As discussed on the forum here, this PR adds two approaches for the sum-of-multiples exercise, along with one article discussing performance differences.

[senekor]

Thanks for writing this up, it was clearly a lot of work and turned out great!

Apart from a few small questions / comments, I'm hesitant to include the performance article in its current state. In my opinion, the following options would make sense:

1. Not include the performance article
2. Leave the benchmarks in there but cut the article down to essentially: "Here are some neat benchmarks, but don't read too much into the numbers, there are simply not enough of them to draw general conclusions."
3. Invest much time and effort to analyze performance over a broad range of inputs, allowing to detect patterns with confidence.

[MatthijsBlom]

There is a fourth option: take this exercise as an excuse for an introduction to benchmarking this kind of stuff in general.

At the end of the day, single benchmarks don't matter much. Nor do the exact big-Os of the various approaches, and neither does which approach is 'best'. In contrast, the process of finding these answers is way more interesting. Even basic understanding of this process is mostly lacking in most programmers. This exercise might offer a nice opportunity: the various approaches are very diverse, the input is straightforwardly variable, and approaches' performance characteristics are tangible.

But yeah, this is probably a lot of work.

[clechasseur]

@senekor Thanks for the comments! I didn't have time to look at this again yesterday, but I'll go over your comments as soon as possible, hopefully tonight. 🙂

[clechasseur]

@senekor I've tried to fix everything you pointed out. I've removed the performance article and instead added a smaller note about complexity and the need for more benchmarks, as you suggested.

If there's anything still missing, don't hesitate! 🙂

[senekor]

Great stuff! Thank you very much 😃

[MatthijsBlom]

Footnotes do not render properly: this document. Clicking the to/from the footnote leads to the top of the page.

[senekor]

Good catch, thanks. I was wondering about this as well and saw that footnotes are in fact used here. Forgot to check again after deployment.

What could be the problem? maybe the missing line ---? I might ask on discord, someone's bound to know the answer.

[senekor]

Actually, on the site I linked, the hyperlinks to/from footnotes don't work either. This might be a general problem of the website.

[senekor]

posted a bug report on the forum https://forum.exercism.org/t/footnote-links-dont-work/9331