Enhanced compatibility

[CensoredUsername]

This adds a bunch of ren'py 7 compatibility back into the main branches. This is mainly meant for games running ren'py 8 but still having older files, and as such we don't have to worry that badly about emitting things that older ren'py's don't quite grok. These changes are surprisingly small and net us compatibility back to at least 6.18 (2014), where the main blocker is old-style screen language. Supporting that is a big burden that I'm not interested in, so around that point sounds like a good cutoff. I also made it generate an error when encountering those that tells people they're using the wrong decompiler version.

Legacy still has its place as it has all the shenanigans needed for --init-offset version checks, --tag-outside-block and friends, old-style screens support, and true compatibility down to 6, but at least this way un.rpyc and the normal tools won't completely balk upon encountering a single file from ren'py 7.

Posting this as a pull request first to maybe get some feedback, but as the changeset is quite small (118+/21-) I feel like it's worth the lower amount of future issue posts to do this.

[CensoredUsername]

Thought about it a bit more, and I'm going to merge this tomorrow. Seems I originally overestimated how much backwards compatibility cruft was necessary when I decided on a hard split for python 3 / ren'py 8. Time to get everything in shape again, and edit the README.

[madeddy]

Seems I originally overestimated how much backwards compatibility cruft was necessary

Me also. If this where much code and work i would vouch against it, but so i see no reason. I'm not sure if this shouldn't sit here a few more weeks, to see if you got everything (code) that's needed for the task. 🤷🏻

In the end, whatever i may think, it's anyway your call as maintainer.

Importantly, seeing new issues the readme gives me the vibe it isn't as clear a it should be.

[CensoredUsername]

I'm not sure if this shouldn't sit here a few more weeks, to see if you got everything (code) that's needed for the task. 🤷🏻

If those appear we can just add them as well. No reason to let this sit and then have to deal with rebasing everything over it.