Mongoose 6.11

• Fix socket leak when there are too many open file descriptors
• Fix publish-subscribe example
• Fix mg_parse_multipart in case of malformed request
• Websocket: Respond to Ping with Pong
• Websocket: Properly close a connection with Close frame (in response to a client's close and when protocol failure is detected)
• Websocket: Fix support of fragmented messages
• Websocket: Add support for control frames interjected in the middle of a fragmented message
• Digest authentication: Fix nonce validity check (expired nonce or nonce from the future did not cause the the check to fail)
• Digest authentication: Fix nonce request value; it worked before because nonce validity check was broken as well
• Digest authentication: Add nonce argument to mg_http_create_digest_auth_header(): clients should use the value received from the server's authentication request.
• Fail if passed a NULL handler to mg_bind or mg_bind_opt.
• Publish sources and tests
• Remove tunneling functionality which was used by nobody
• Add UDP client example
• Don't use user_data in mqtt server
• Deprecate mg_http_parse_header() and implement mg_http_parse_header2() instead, which allocates a new buffer if the client-provided one is not large enough (similarly to asprintf).
• Fix limitations of header value lengths, e.g. when parsing authentication headers such as nonce, etc.