#682 Add created() function for sprites

New function added:
  bool created(void);
to check if sprite has been rotated. Example:

if ( !spr.created() ) Serial.println("Sprite has not been created");

examples/DMA test/SpriteRotatingCube/SpriteRotatingCube.ino

@@ -6,7 +6,7 @@
 // parallel TFT's (tested with ILI9341 and ILI9481)
 
 // The sketch will run on processors without DMA and also parallel
-// interface TFT's. Comment out line 25 for no DMA.
+// interface TFT's. Comment out line 29 for no DMA.
 
 // Library here:
 // https://github.com/Bodmer/TFT_eSPI