code: function flipBufferHorizontally(buffer) {
    return makeBuffer(buffer.width, buffer.height, function(context) {
      context.scale(-1, 1);
      context.drawImage(buffer, -buffer.width, 0);
    });
  }
docs: Make a horizonally-flipped copy of a buffer or image.
  @param {external:canvas|external:image} buffer The original image
  @return {external:canvas} The flipped buffer