Added to_image( *args )
 This is a public method that returns the QR Code you have
 generated as an RMagick ImageBlob. It can be sent to a browser, sent to a mobile device or
 saved to a file for output. this format can be read by a decoder

 It takes 4 arguments, {file_type=>'jgp|gif|png',:dimension=><pixel_width>
 :bgcolor=>'white|black|red|blue', :color=>'black|white|red|blue'

 instance._to_image( :file_type => 'jpg', :bgcolor => 'red', :color=>'black') =>  String
  The calling program could then write the blob to file:
   code = File.new('qrcode.jpg')
   code.write(instance.to_image())
   code.close => the file now an image of the QRCode
added test for to_image. It only checks that a string is returned, TODO: need more validation on the output