Change ArrayBuffer handling

[fetimo]

Fixes #47

[fetimo]

I've added a few tests for the importImageFileToBase64 helper. I also found that it was needed to check the runtime so I added a helper for that.

I did try to use const binary = new TextDecoder('latin1').decode(imageUint8); for the browser branch but in testing I got an error when trying to convert it to base64. The looping version doesn't have this issue and also allows for much larger file sizes.

The image test bytes are based on https://github.com/mathiasbynens/small/blob/master/jpeg.jpg and https://evanhahn.com/worlds-smallest-png/

Feedback is very welcome :)

[Balearica]

Thanks for contributing, I will try and review this week.