Add changeset for stamp size fix

Author: mikebarkmin

.changeset/stamp-size.md

@@ -0,0 +1,18 @@
+---
+type: patch
+---
+
+Draw stamps at the sprite's size.
+
+A sprite scaled with `setSize` left stamps at the costume file's natural size:
+shrink a sprite to a quarter and every stamp it left behind was still four
+times too big. The stamp was drawn straight from the untouched source image,
+which ignores the costume's current width and height.
+
+Stamps now use the costume's size, so a stamp looks like the sprite that left
+it.
+
+A stamp drawn more than once also kept turning. Each draw subtracted 90 degrees
+from the stamp's own heading and stored it back, so the angle drifted a quarter
+turn per frame and a stamp on screen spun. The heading is now worked out
+without changing the stamp.