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* upstream/master: (72 commits)
  Typo error in ESP8266WiFiGeneric.h (esp8266#7797)
  lwip2: use pvPortXalloc/vPortFree and "-free -fipa-pta" (esp8266#7793)
  Use smarter cache key, cache Arduino IDE (esp8266#7791)
  Update to SdFat 2.0.2, speed SD access (esp8266#7779)
  BREAKING - Upgrade to upstream newlib 4.0.0 release (esp8266#7708)
  mock: +hexdump() from debug.cpp (esp8266#7789)
  more lwIP physical interfaces (esp8266#6680)
  Rationalize File timestamp callback (esp8266#7785)
  Update to LittleFS v2.3 (esp8266#7787)
  WiFiServerSecure: Cache SSL sessions (esp8266#7774)
  platform.txt: instruct GCC to perform more aggressive optimization (esp8266#7770)
  LEAmDNS fixes (esp8266#7786)
  Move uzlib to master branch (esp8266#7782)
  Update to latest uzlib upstream (esp8266#7776)
  EspSoftwareSerial bug fix release 6.10.1: preciseDelay() could delay() for extremely long time, if period duration was exceeded on entry. (esp8266#7771)
  Fixed OOM double count in umm_realloc. (esp8266#7768)
  Added missing check for failure on umm_push_heap calls in Esp.cpp (esp8266#7767)
  Fix: cannot build after esp8266#7060 on Win64 (esp8266#7754)
  Add the missing 'rename' method wrapper in SD library. (esp8266#7766)
  i2s: adds i2s_rxtxdrive_begin(enableRx, enableTx, driveRxClocks, driveTxClocks) (esp8266#7748)
  ...