16 bit support for output images

[Jon12344212]

Have been using the program on a non-AVX PC for a couple of days now and seems to be working well, although obviously slow. One thing I wish was supported was 16 bit image output. It's nice that it supports lossless compression PNG, but would be nice if inputting a 16 bit PNG that it would come out also as 16 bit instead of 8 bit. Thank you.