Fixes#5116Fixes#2743
The Arduino WiFiClient object allows sending the same packet to all
connected clients of a WiFiServer. In their implementation it may make
sense, but on the 8266 with things like SSL it doesn't.
Update the docs to note that WiFiServer::write() is a no-op, and that
the app should use the WiFiCliebnt::write() on all connected clients as
appropriate.