Added blending operators to png and svg

Also refactored to start using save/restore more often

samples/load_images.rb

@@ -1,7 +1,7 @@
 require 'squib'
 
 Squib::Deck.new(width: 825, height: 1125, cards: 1) do
-  background color: :white
+  background color: '#0b7c8e'
   rect x: 38, y: 38, width: 750, height: 1050, x_radius: 38, y_radius: 38
 
   png file: 'shiny-purse.png', x: 620, y: 75
@@ -19,5 +19,9 @@ Squib::Deck.new(width: 825, height: 1125, cards: 1) do
   # relative to the SVG page. See this example in an SVG editor
   svg file: 'offset.svg', id: 'thing',  x: 0, y: 0, width: 600, height: 600
 
+  # Over 15 different blending operators are supported. See http://cairographics.org/operators
+  png file: 'ball.png', x: 50, y: 700
+  png file: 'grit.png', x: 70, y: 750, blend: :color_burn
+
   save prefix: 'load_images_', format: :png
 end