Add ARTI-FX to esp8266_4MB_M (experimental!)
Arti.h
- FREE_SIZE ESP.getFreeHeap() for 8266
- define asChar(x) to print to Serial/File depending on ESP32/8266
- artiPrintf: print to USER_PRINTF (experimental)
Arti_wled.h
- add ARDUINO_ARCH_ESP8266 to ARTI_ARDUINO
- add soundPressure
usermod_v2_artifx.h: use FREE_SIZE