Fix a lot of typos and add words to dictionary to simplify spell checking

[ThisFunctionalTom]

Hi Zaid,

I went through all of markdown files with the "code spell checker". He found a lot of typos. I added some words which I thought are correct in the folder dictionary so that they are not marked as errors.

Please tell me if it is to big pull request and I will try to split it up.

I changed also a few places in the source code. I hope this is OK?

FYI, I had following workflow:

• Open all files from a chapter by selecting them, right click and open to the side.
• In each file press F8 to jump to the next spelling error
• Press ctrl+. to open suggestion and correct the error or add the word to local folder
• Save and close the file, repeat for all open files
• Repeat for all chapters :-)

I hope this helps a little bit.

[Zaid-Ajaj]

This is really awesome work, Tomas 😍 thank you so much, really appreciate it :pray: I will start using this spell checker from now on, looks like my writing absolutely needs it ;)