Expand Chapter 13 to align with lecture content and quiz (wire formats, schemas, REST/SOAP, etc.)

[talosgl]

This PR expands Chapter 13 of the book to clarify and contextualize concepts mentioned in the video lectures and quizzes linked to on the lesson page. Key changes:

• Adds introductory explanations for wire formats, serialization, and deserialization
• Introduces schemas (XSD, JSON Schema) and their role in validation
• Adds comparison of SOAP vs. REST architectural styles
• Adds glossary entries for new terminology (e.g. wire format schema, serialization)
• Adjusts flow of "Application Programming Interfaces" section for clarity
• Adds a sentence on Google API rate limits and Twitter OAuth, as these are referenced in the quiz
• Includes a link to the Roy Fielding REST interview used in Coursera, for quiz context (separate commit in case this was too far)

The changes aim to keep the chapter concise and readable while filling in gaps between text, video, and quiz content.