Arithmetic coded JPEG support

Arithmetic coding is a part of the JPEG standard. All the related patents are expired years ago. Most of the software don't support such JPEGs, but still it would be nice if it will be supported as input for lossless conversion from JPEG to JPEG XL, just to be sure that any valid JPEG can be converted losslessly.

As far as I understand, it won't be possible to restore original JPEG file in this case, because all the stored information about original JPEG file is Huffman related. But I think, it would be enough to preserve just image data without possibility to restore exactly original JPEG file (like in #80).

I posted some examples of arithmetic coded JPEGs [here](https://bugs.chromium.org/p/chromium/issues/detail?id=669501#c3).