Support Uint8ClampedArray

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I want to be able to load and save images using a [Uint8ClampedArray](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8ClampedArray). Such array stores the red, green, blue and alpha of each pixel in the image from left to right, then top to bottom. This is similar to how `image.bitmap.data` works.

**Describe the solution you'd like**
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Support passing a Uint8ClampedArray to `Jimp.create` and add `image.getUint8ClampedArray()`.

**Describe alternatives you've considered**
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[Manually parsing them](https://github.com/Richienb/render-gif/blob/f881b8adeb5d85f0f72169f764a9b837b6327393/index.js#L22-L29), adding each pixel one at a time to the image.

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