[Proposal] Features for tool-assisted speedrunning

[jgcodes2020]

A few members of the SM64 tool-assisted speedrunning community have been working on this fork of mupen64plus's core: Mupen64-Rewrite/mupen64plus-core-rr.

As-is, attempting to merge this repo would be a disaster, and it might not align with this project's scope. I also think some features we implemented are far too high-level to be directly implemented on the core side.

These are the features I'd like to add; they make up the bare minimum needed to implement other high-level TASing features.

• An input callback that allows the frontend to filter or override inputs, per-controller. This is used for recording and playing back TASes, as well as with custom scripts that help us make TASes.
• A way to capture audio data in the frontend. This is used to encode videos of a TAS. Our fork does this with two callbacks: one receiving sample data, one receiving changes to sample rate. (can be fixed by [WIP / RFC] New audio backend API #79)
• A way to directly access RAM (as opposed to indirectly via the cheat engine). This is needed for some custom scripts which read game variables. (the debugging API might be sufficient?)

[jgcodes2020]

closed, will make proper issues later