Python books fixed

[TimoSalomaki]

What does this PR do?

Add Resource(s) | Remove Resource(s) | Add info | Improve Repo

For resources

Description

• Removed The Python Ecosystem: An Introduction. It was 404, but I could find a working version on archive.org. However, it was a medium-length article, not a book in any way or form.
• Fixed some O'Reilly and other non-functioning links.
• Fixed the Hacking Secret Cyphers with Python book link, as it seems to be called Cracking Codes with Python now. Or maybe it's just a different book. Regardless, the link works and leads to a free ebook on the topic.

Why is this valuable (or not)

How do we know it's really free?

For book lists, is it a book?

Checklist:

• Not a duplicate
• Included author(s) if appropriate
• Lists are in alphabetical order
• Needed indications added (PDF, access notes, under construction)