Added column_gutter_grid example

examples/grid/column_gutter_grid.rb

@@ -0,0 +1,20 @@
+# encoding: utf-8    
+
+require "#{File.dirname(__FILE__)}/../example_helper.rb"
+
+Prawn::Document.generate('column_gutter_grid.pdf') do |p|
+  p.define_grid(:columns => 3, :rows => 10, :column_gutter => 10)
+
+  p.grid.rows.times do |i|
+    p.grid.columns.times do |j|
+      b = p.grid(i,j)
+      p.bounding_box b.top_left, :width => b.width, :height => b.height do
+        p.text b.name
+        p.stroke do
+          p.rectangle(p.bounds.top_left, b.width, b.height)
+        end
+      end
+    end
+  end
+end
+