When DEBUG_HEAP is defined, add free heap bytes to every log line in RedirectablePrint::log_to_serial

platformio.ini

@@ -55,6 +55,7 @@ build_flags = -Wno-missing-field-initializers
 	-D MAX_THREADS=40 ; As we've split modules, we have more threads to manage
 	#-DBUILD_EPOCH=$UNIX_TIME ; set in platformio-custom.py now
 	#-D OLED_PL=1
+	#-D DEBUG_HEAP=1 ; uncomment to add free heap space / memory leak debugging logs
 
 monitor_speed = 115200
 monitor_filters = direct