advanced logging

###standard logging for standard logging puposes you can use the "webserial" versions. As long as the esp connected to wifi logmessages are accessible under /webserial, linked at status page.

###advanced logging in case of problems with wifi connection failures, randomly network disconnects or other depper problems the webserial version will not help. In this case you need an additional ESP8266 which works as transparent bridge for the serial monitor.

1. go to https://github.com/jeelabs/esp-link,
2. flash esp-link on your ESP8266 (now named as ESPLink), check the esp-link readme as HowTo
3. start your ESPLink and configure it:
   1. enable STA-Mode and connect it with your local WLAN (Page: Wifi-Station)
   2. select Pin Assignment -> preset: ESP12-swapped (page: Home)
4. connect your ESPLink to ModbusGateway like this:

Pin	ModbusGateway	ESPLink
RX	GPIO-1 (TX0)	GPIO-13 (RX0)
TX	GPIO-3 (RX0)	GPIO-15 (TX0)
3.3V	3V3	3V3
GND	GND	GND

Go to your ESPLink, uc-Console, check Baud: 115200 and enjoy your ModbusGateway Log