Adding Excel xlsx support and prefixed images

* New sample!
* New API function!
* Ignoring _img in samples

bin/squib

@@ -1,36 +1,2 @@
 #!/usr/bin/env ruby
 require 'squib'
-require 'cairo'
-
-red = [1.0, 0.0, 0.0, 1]
-white  = [1.0,1.0,1.0, 1]
-
-surface = Cairo::ImageSurface.new(825,1125)
-cr = Cairo::Context.new(surface)
-
-#Set white background
-cr.set_source_rgba(*white)
-cr.paint
-
-#Write some text
-cr.set_source_rgba(*red)
-cr.select_font_face ("Helvetica");
-cr.set_font_size(36)
-cr.move_to(150,150)
-cr.show_text('Hello, World!')
-
-#Put our own image here
-if File.exists? 'test.png'
-  png = Cairo::ImageSurface.from_png('test.png')
-  cr.set_source(png, 0, 300)
-  cr.paint
-end
-#Save!
-cr.target.write_to_png("test.png")
-
-puts "Done!"
-
-#font type: 'Rockwell'
-#set_font type: 'Rockwell'
-#set_font type: 'Rockwell'
-