General language and structure improvements

This PR includes many small-ish changes:

• Fixing typos
• Grammar/punctuation improvements
• Fixing formatting of lists
• Converting HTML tables to Markdown
• Making plain URLs into clickable links
• Re-ordering paragraphs in the page about Ion

It also significantly changes page ch13-03.

Each commit's message explains/justifies that commit's changes.

The book builds fine after these changes, but the CI pipeline is broken so it fails anyways.