Update "Processing for HTML output"

1. Use percent-encoding for URLs
2. Escape single and double quotes always as per OWASP recommendations
   (not just in HTML attribute values)
Use URL-escaping for all links
Handle escaped '<' characters in finding the end of the paragraph
Code-span detector: Backticks are not "escaping" backticks when within a code-span
Minor edit for clarity regarding invalid UTF-8 bytes