v4.6.0

Removed

• scrape_as_html. Use scrape_as_markdown with format: 'html'.
• extract.
• WEB_UNLOCKER_ZONE. The server no longer uses or creates a Web
  Unlocker zone. The variable is ignored if set.

Changed

• A usage limit (client_10100) always returns Usage limit reached,
  naming both causes: free credits or funds used up, or a zone limit.
  It no longer guesses Free credits used up from the zone name.