ARTI-FX support 8266 (experimental!!) add soundpressure

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

wled00/FX_2Dfcn.cpp

@@ -583,7 +583,6 @@ bool Segment::jsonToPixels(char * name, uint8_t fileNr) {
       }
     }
   }
-  USER_PRINTLN();
 
   releaseJSONBufferLock();
   return true;