`eigmax` and `eigmin` claim complex numbers cannot be sorted

[araujoms]

The docstrings of eigmax and eigmin write that "Note that if the eigenvalues of A are complex, this method will fail, since complex numbers cannot be sorted.". This is nonsense, the complex numbers are a totally ordered set. I'd like to fix that. There are two solutions:

1. Rewrite the docstring to say that there is no canonical order for the complex numbers.
2. Change the function to start sorting complex numbers (by lexicographical order, for instance).

I think the latter is more useful, but I'm also fine with the former. Opinions?

[ViralBShah]

Cc @stevengj