Edit chap02

[SarveshMD]

Fixed a lot of things in chap02.md.

• Covered variables and reserved words with backquotes
• Corrected indentation
• Changed year in privacy.php from <p>Last edited: 07-July-2020</p> to <p>Last edited: 07-July-2021</p>. I just assumed that it was 2021, and changed it. If what I assumed was wrong, let me know and I'll push another commit un-doing that change.
• etc.

BTW, if someone else is reading this at 13:21 pm UTC July 29, head on to https://youtu.be/CQVbRc50BNo to watch @csev's live coding session on YouTube :)

[csev]

Thank you :) Merged live on a stream.