#5 expose SID register statuses

[Stian Skjelstad]

I want to move my project from libsidplay 1.x into libsidplayfp. My project exposes the internal statuses of the SID chip, which libsidplayfp hides away, Attached is a suggestion for how to expose this, and API example is patched into the sidplayfp utility.

Another status that could be added is the current ADSR and volume.
ADSR could be a simple enum. This however would need to be patched into each engine, which is more work than the what the patch expose, which is only the latest status of each register (and hints if any of the important control flags has been toggled)

[Leandro Nini]

Currently the project is in strict bugfixing mode, no API change is planned in the near future unless someone would like to step up as maintainer. I'll leave this here in case, thanks.