Remove convenience functions - only read from input functions.
Use on input function instead of read_func/seek_func
Type fixes, fixes for Emscripten
Update warning message
Test invalid png files
* Emscripten: don't decode resources in the browser
Convert YCbCr to RGB by data block rather than by row
* Saves memory and is more accurate, but may be slower
* Seems to be what modern JPEG decoders do
Update jpeg tests
Code style: null checks