Permission handling added

- Updated section 4. Security and privacy considerations
- Added interface TCPPermission (UDPPermission and TCPserverPermission remains but wants to get feedback before going further)
- Editorial corrections
https://github.com/sysapps/tcp-udp-sockets/issues/81
What are your thoughts on requesting permission, and retrieving permission state for, multiple endpoints in a single call? Does it make sense for a site to be able to retrieve the complete set of endpoints it has access to?