Fixes #271

[jens-struct]

@zachleat This is the PR for #271, it optimizes the js api for cropping.

I left some comments in the code to start some discussions.

[jens-struct]

Instead of this we could duplicate the logic of https://github.com/11ty/eleventy-img/blob/main/src/image.js#L142 here, but this would mean a not pretty workaround like:

    transform: {[cacheKey]: function(sharp, stats) {
      sharp.resize({
        width: stats.width,
        height: Math.floor(stats.width / cropRatio),
        fit: Sharp.fit.cover,
        position: Sharp.strategy.entropy,
      });
    }}[cacheKey],

where:

  cacheKey: 16 / 9

is way cleaner if you ask me 😅 So i arrived at the solution i pushed here, to be able to influence the hash part of the filename if needed. Please see the sample-crop.js for the usecase.

Also the naming of this option could maybe be improved, i.e. hashKey?

[jens-struct]

This removes all widths that would cause upscaling of the original image.

I could probably go a step further and try to build this kind of sanitization into 11ty image.

[jens-struct]

This gets the max width for cropping without upscaling the original image.

I guess this is also a nice thing to have in the core? Although an opt-in through an option is probably a good idea, as it is likely not the wanted behavior for all usecases.

[jens-struct]

Probably better to pass a clone instead of a reference here?

[zachleat]

Shipping as manualCacheKey and a limited set of width, height, format passed into the transform callback in Image v7.0.0-alpha.5.

Thank you!