Bypass transform

[Jamie0]

We use express-sharp to serve images. One problem we face is that there is no mechanism in express-sharp to bypass transformation, so we cannot serve animated GIFs from the same endpoint (without a middleware costing a double hit to storage).

As libvips has no [planned] support for animation, it would be useful if there was either a search parameter to bypass transform and just return the raw image, or if express-sharp could detect the prescence of an animation and bypass transformations for that file.