[Csnd-dev] subinstr

I was looking at an issue just opened on subinstr, and I was wondering whether we could mark it as deprecated (but of course keep it in the code). 

This was introduced before UDOs, which do a much better job, and now with Csound 7.0, instruments are more flexibly handled.

Trying to keep patching it to behave correctly takes a lot of effort, as the design was not great to start with.

Victor