Working on adding full Sixel support

Working on adding support for the other mainstream terminal pixel protocol of the main two - Sixel. Already did fully implemented the kitty protocol last time, so once I’m done with this one, I’ll be done with terminal protocols (at least for the near future, hopefully). There are some other ones like the iterm2 protocol, but that one’s pretty rare and I won’t add it unless I really don’t have anything better to do.

It’s basically done, just need to polish it and test it on a bunch of terminals and operating systems to make sure everything works before merging.