Upgrade to SDL 2

[roncli]

https://wiki.libsdl.org/SDL2/MigrationGuide

[roncli]

Motivation behind this is that there have been reports that SDL 1.2 is causing performance issues with modern computers. Most notably rethink has a major issue with it.

[SiriusTR]

It appears that SDL2 discontinues the CD Audio API, meaning Redbook will likely no longer work (unless that uses a different API). Notably, Rebirth would already be affected by this if that is the case.
Is that a problem for anyone we know of? It isn't for me.

[roncli]

I would not feel right disabling Redbook audio. Let me ask 8bit how they fixed it.

[roncli]

Apparently "you can make a Redbook style soundtrack addon or use the Jukebox". So, added work would have to go in to keeping Redbook audio. That's a bit beyond what I know how to do, so I'll keep this open in case someone is able to SDL 2 working. My experiment with that went... well, it didn't go at all, actually. 🙃