time: import IANA timezone definitions, expose SNTP API (#6373)

* time: import IANA timezone definitions
- `configTime("timezone", "ntp servers...")` added
- timezone definitions by country/cities (TZ.h)
- script to update timezone definitions
- updated example

* fix former configTime non-matching signature

* +include

* example: add scheduled function in callback

* crlf fix

* +missing license for napt

* SNTP: expose configuration helpers

* update submodule

* update precompiled libraries

* optional: change SNTP startup delay

* makes SNTP_UPDATE_DELAY a weak function
update example
fix for lwip1.4

* on the proper use of polledTimeout api... thanks @mcspr :]

* improve update script (per review)

* update lwIP submodule

* update submodule

* hide harmless shell message

* update the release process by asking first to update TZ.h
[ci skip]

* minor update in release documentation

* update in release documentation

* update in release documentation

* clarify release documentation

* fix release documentation - sorry for the noise :(

* fixes per review

* example style

* useless variable in example

* update lwip2 submodule reference, to include espressif missing declaration fixes

cores/esp8266/Arduino.h

@@ -275,10 +275,13 @@ long secureRandom(long);
 long secureRandom(long, long);
 long map(long, long, long, long, long);
 
-extern "C" void configTime(long timezone, int daylightOffset_sec,
-    const char* server1, const char* server2 = nullptr, const char* server3 = nullptr);
+void configTime(int timezone, int daylightOffset_sec, const char* server1,
+    const char* server2 = nullptr, const char* server3 = nullptr);
 
-#endif
+void configTime(const char* tz, const char* server1,
+    const char* server2 = nullptr, const char* server3 = nullptr);
+
+#endif // __cplusplus
 
 #include "pins_arduino.h"