Antoine Collas

Ok, I see. I'll try to do something like `PSDFixedRankComplex` !

@nkoep I rewrote most of the PR to take into account your remarks. Especially the classes of the complex-valued manifolds inherit from the real-valued ones (as suggested by `PSDFixedRankComplex` and...

@nkoep, I addressed all the changes you required. Tell me if it is ok for you!