ESP32 module price is now within range of 8266 price.
ESP32 capability and OS support is hugely better than 8266,
we can support mbedtls tls, http/2 etc with ESP32.
I'm no longer testing on ESP8266... there's no more
user traffic... it's time to go.
This enables selected things from -Wextra, can't use -Wextra because it is
fussy enough to complain about unused params on functions... they are
there for a reason.
-Wsign-compare
-Wignored-qualifiers
not -Wimplicit-fallthrough=3 ... only on gcc 7
-Wtype-limits
-Wuninitialized
not -Wclobbered ... only on gcc 7ish
fix the warnings everywhere they were found.