Restructure chapter 2

[tshiya731]

Hi Robert, this is the restructure for chapter 2 and 3. As we discussed, for chapter2, the original module section is deleted, and will be added in later book. And for chapter 3, the debugging section is removed because it will appear later. Also, the corresponding additional learning material is revised too.

But also, there is still some things to be done in these two chapters:

1. can you please fill the description .md files?
2. for chapter 3, i am not sure if the name is good enough.
3. for chapter 3, it seems you need to combine the debugging sections into error chapter, or should it be done when all the restructure is done?

@rlanzafame

[rlanzafame]

In this PR you are merging restructure-book into main but that won't happen until we are ready to release the book once it has been entirely restructured. For next round of edits, it would be good to make a new branch and create a pull request from that branch into the branch restructure-book (not into main). I'll change the branch rules. This makes it easier to keep track of more than one task at a time. After making this comment I will close this PR because all of the commits will be in restructure-book branch already, and once you make some new commits (on a new branch!) you'll be able to create a new PR. You can still comment here. Message me separately if you need help setting up a new branch and PR.

• by descriptions .md do you mean the main page for each chapter? I added a small note for the new one (changed Advanced to Beyond the Basics)
• adapted file names and titles of chapters and sections
• Yes, I'll make a new error chapter, but can't right now...maybe just add a short note here about where the material is (which file) and where you think it should go, then i can take the next step.
• there is "additional material" at the end of the last section of each chapter, but it is relevant for the whole chapter. I think we can add it to the main page for the chapter or the Exercises page (at the bottom of the page in both cases)...what do you think?
• there is a heading level issue. let's solve it as part of the restructure, but can postpone it a bit (i created an Issue Fix header level increase on pages #35 )