Adding in alpha transparency to png

lib/squib/api/image.rb

@@ -1,10 +1,10 @@
 module Squib
   class Deck
     
-    def png(range: :all, file: nil, x: 0, y: 0)
+    def png(range: :all, file: nil, x: 0, y: 0, alpha: 1.0)
       range = rangeify(range)
       file = fileify(file)
-      range.each{ |i| @cards[i].png(file, x, y) }
+      range.each{ |i| @cards[i].png(file, x, y, alpha) }
     end
 
     def svg(range: :all, file: nil, x: 0, y: 0)

lib/squib/graphics/image.rb

@@ -1,11 +1,11 @@
 module Squib
   class Card
 
-    def png(file, x, y)
+    def png(file, x, y, alpha)
       cc = cairo_context
       png = Cairo::ImageSurface.from_png(file)
       cc.set_source(png, x, y)
-      cc.paint
+      cc.paint(alpha)
     end
 
     def svg(file, x, y)