Rewrite existing credits

Each credit has its own draw function

Credits outside of the visible game area are not drawn

modules/dom/canvas.scm

@@ -39,7 +39,8 @@
             translate!
             rotate!
             set-transform!
-            set-image-smoothing-enabled!))
+            set-image-smoothing-enabled!
+            measure-text))
 
 ;; HTMLCanvasElement
 (define-foreign get-context
@@ -98,3 +99,6 @@
 (define-foreign set-image-smoothing-enabled!
   "canvas" "setImageSmoothingEnabled"
   (ref extern) i32 -> none)
+(define-foreign measure-text
+  "canvas" "measureText"
+  (ref extern) (ref string) -> (ref extern))