[sdlsound] SID decoder?

[Ryan C. Gordon]

> The open-source libsidplay library is available to decode .SID files.
> Do you think it would be a good idea to incorporate libsidplay into
> SDL_Sound?  Or are chiptune emulators abit out of our scope, per se?

I've been wanting to do this, but never got around to it. I figure it's of
limited use for games, but that doesn't mean it shouldn't be done. I'll
accept any patches that support this.

--ryan.