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

usermods/usermod_v2_four_line_display_ALT/usermod_v2_four_line_display_ALT.h

@@ -1419,7 +1419,7 @@ class FourLineDisplayUsermod : public Usermod {
         if (pinsChanged || type!=newType) {
           if (typeOK) {
             typeOK = false;
-            if (u8x8 != nullptr) delete u8x8;
+            if (u8x8 != nullptr) delete u8x8; //WLEDMM warning: deleting object of polymorphic class type 'U8X8' which has non-virtual destructor might cause undefined behaviour [-Wdelete-non-virtual-dtor]
             u8x8 = nullptr;
             USER_PRINTLN(F("Display terminated."));
           }