EspSoftwareSerial release 5.2.1 (esp8266#6219)

* Track breaking API chance in EspSoftwareSerial.

* Revert "Track breaking API chance in EspSoftwareSerial."

This reverts commit 78aa3e8.

* Track breaking API chance in EspSoftwareSerial.

* Bug fix in EspSoftwareSerial

* EspSoftwareSerial: improved memory fences

* Refactoring upstream

* EspSoftwareSerial fixed a high-bitrate error source, probably caused by end-bit detection

without checking for same-level timestamps from the IRQ

* EspSoftwareSerial examples updates

* Fix to stop bit detection in EspSoftwareSerial

* Latest bit timings fix in EspSoftwareSerial.

* EspSoftwareSerial examples

* EspSoftwareSerial latest throughput results in comments of loopback.ino

* Lastest EspSoftwareSerial, dependent on a few as yet unmerged PRs, tho

* Submodule EspSoftwareSerial release 5.2.0 with workaround for as yet missing attachInterruptArg in Arduino.h

* EspSoftwareSerial release 5.2.0, includes workaround for missing attachInterruptArg in ESP8266 Arduino

* EspSoftwareSerial: CI failed on examples - defines for Wemos board GPIOs.

libraries/esp8266/examples/SerialStress/SerialStress.ino

@@ -72,8 +72,8 @@ void setup() {
 
   // using HardwareSerial0 pins,
   // so we can still log to the regular usbserial chips
-  SoftwareSerial* ss = new SoftwareSerial(3, 1);
-  ss->begin(SSBAUD);
+  SoftwareSerial* ss = new SoftwareSerial;
+  ss->begin(SSBAUD, 3, 1);
   ss->enableIntTx(false);
   logger = ss;
   logger->println();