• Internal core has been changed from blocking, thread-per-connection to
  non-blocking, asynchronous, one thread for all.
• API modification for server creation and response creation. That allowed
  keep-alive support for dynamic requests, boosting the embedded performance
  to 100+ thousands requests per second on a single core
  (as measured on my development MacBook laptop)
• Unified handling of POST requests and Websocket requests by putting a
  payload into conn->content, conn->content_len attributes.
  That simplified user code and eliminated the need of mg_read(),
  since mongoose buffers all data prior to calling the callback
• Keep-alive support is the default
• Dropped SSI support and throttling support
• Several configuraition parameters are gone:
  • cgi_environment (replaced with MONGOOSE_CGI),
  • protect_uri (not useful)
  • ssi_pattern (SSI support is gone)
  • throttle (throttling support is gone)
  • error_log_file (not used)
  • enable_keep_alive (enabled by default)
  • listening_ports (renamed to listening_port)
  • num_threads (core has changed to single thread)
  • put_delete_auth_file (renamed to dav_auth_file)
  • authentication_domain (renamed to auth_domain)
• Due to the async, non-blocking nature of the core, few restrictions
  are now in place:
  • user callbacks must not block
  • POST and Websocket data are now buffered, and cannot be huge
• mongoose is now capable on listening on only one port