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
Wildcards make it possible to request permission for multiple endpoints at once, but they don't allow retrieving the current set of allowed endpoints. This is a known hole in the Permissions API, which I'm wondering about (and haven't solved yet) for Web Bluetooth as well. I think Web Bluetooth will just provide a function to retrieve a sequence of already-allowed devices.

Obviously there's no need to add this function before merging this PR; it's just something to think about.