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
See my comment at https://github.com/sysapps/tcp-udp-sockets/issues/81#issuecomment-66998129. Which is your general view on security/permissions for this API?