esp_yield() -> delay()

[d-a-v]

This is an internal change proposal aimed at being compatible with

• esp8266 arduino core v3.1 (to come)
• esp8266 arduino core <= 2.7.4 (with lwip1.4)

Packet capture facility is added in the simple example to show live ICMP captured packets during operations.

A proposal will come very soon is made in the esp8266 arduino core for this library to work with

fixes #41 fixes #40 fixes #37 replaces and closes #27

[rednebmas]

Thank you @d-a-v. For those of you that wish to use this branch with PlatformIO, you can replace dancol90/ESP8266Ping@^1.0 under libdeps in platformio.ini with https://github.com/d-a-v/ESP8266Ping.git#esp8266arduinocorev3

[dancol90]

Fixed in #46