Add support for ImageData and fix a hang in buffer handling

[WintrySnowman]

Addresses two concerns:

1. The setImage() function started to hang for a long period of time (several seconds for a 1080p image, for example) trying to handle the buffer. I don't quite know why the code was written as it was originally, but changing that one line has stopped it hanging.
2. Adds support for the ImageData obtained from canvases. This improves performance by allowing you to bypass toBlob()/toDataURL() (which would convert to a PNG first), if that's the data format you already have.

[Balearica]

Thanks for this contribution. I agree that it makes sense to pass ImageData directly rather than converting to .png.

[Balearica]

This had to be reverted as it does not run on Node. 100% my fault for not checking first, however in the future please run the automated tests before making a PR (npm run test).