Allow for inverting a complex matrix

[mmtrebuchet]

I see that invert is "Currently only defined for general real matrices". I don't have a good linear algebra intuition, and I can't see why the invert() function in linalg.d isn't capable of handling complex arguments. Everything I've seen suggests that ZGETRF and ZGETRI should invert a complex matrix. Is there something I'm missing?

[kyllingstad]

To be honest, I don't know. I would guess that I had some reason to put the !scid.core.traits.isComplex!T constraint on the function at the time, but it's so many years ago that I don't remember anymore. And I agree, at a quick glance it does seem like it should work with complex types. If you confirm that this is the case, a pull request (with a unittest) that removes the comment and the constraint would be much appreciated!