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
The Chrome Apps sockets API includes wildcards in its permissions: https://developer.chrome.com/apps/app_network. Is that something you'd want to include here?