Are `out` parameters supported at all?

It appears that at least some work was started on supporting out parameters in conf files in branch pmacheta/inout but it's not clear if that was ever integrated back into master.

I'm working on tracing a 3rd party library that uses out parameters rather extensively. Implementing the functionality may not be out of the question for me, but if there is existing work I'd prefer to build on it. Or, if the existing work has problems or ran into roadblocks, it would be good to know that, too. I will have to implement something, and would prefer to implement something reusable by extending ltrace than something bespoke just for my situation.