Added POV image effect

Setup is really easy, after first boot and WiFi/LEDs setup:
go to wled.local/edit and upload a couple image to WLed's filesystem.
Only PNG is supported right now, further support for GIF is planned.
The image should be as wide as the 1D segment you want to apply to.

When done, go to the Effect page on the UI, select "POV Image" effect.

You could also update the image with a post to the JSON-API like this:
curl -X POST http://[wled]/json/state -d '{"seg":{"id":0,"fx":114,"f":"/axel.png"}}'

The segment should move at around 120RPM (that's 2revolutions per seconds) for an image to showup.
More informations and pictures here : https://lumina.toys

wled00/usermods_list.cpp

@@ -210,6 +210,10 @@
   #include "../usermods/LDR_Dusk_Dawn_v2/usermod_LDR_Dusk_Dawn_v2.h"
 #endif
 
+#ifdef USERMOD_POV_DISPLAY
+  #include "../usermods/pov_display/usermod_pov_display.h"
+#endif
+
 #ifdef USERMOD_STAIRCASE_WIPE
   #include "../usermods/stairway_wipe_basic/stairway-wipe-usermod-v2.h"
 #endif
@@ -454,4 +458,8 @@ void registerUsermods()
   #ifdef USERMOD_LD2410
   usermods.add(new LD2410Usermod());
   #endif
+
+  #ifdef USERMOD_POV_DISPLAY
+  usermods.add(new PovDisplayUsermod());
+  #endif
 }