lwip2 fixes and time/ntp management

core: +settimeofday()
core: +coredecls.h +sntp-lwip2.c
core: fix clock_gettime() with micros64()
core: honor DST in configTime()
core: internal clock is automatically started
examples: +esp8266/NTP-TZ-DST.ino
lwip2: sntp client removed
lwip2: fix crashing with WiFi.softAPConfig(ip,ip,ip)
fix #3852

Author: d-a-v

cores/esp8266/coredecls.h

@@ -0,0 +1,9 @@
+
+#ifndef __COREDECLS_H
+#define __COREDECLS_H
+
+extern bool s_bootTimeSet;
+
+// TODO: put declarations here, get rid of -Wno-implicit-function-declaration
+
+#endif // __COREDECLS_H