Extract duplicate arithmetic decoder to own class
Removing set-presence-in-ImageData check from canvas.js
update comments
Follow JMPR op only if outside of FDEF and IF
Merge pull request #4446 from benbro/master

Follow JMPR op only if outside of FDEF and IF
Merge pull request #4431 from fkaelberer/ExtractArithmeticDecoder

Extract arithmetic decoder to own file
Merge pull request #4420 from prometheansacrifice/RemovingCheckSetPresence

Removing set-presence-in-ImageData check from canvas.js