logabsdet for complex matrices

[garrison]

logabsdet is a function that returns (log(abs(det(M))), sign(det(M)) but may provide increased accuracy and/or speed (and is less likely to overflow). At the moment it works only for real matrices, but I believe it would be great if it were implemented also for complex matrices.

From glancing at the code (and earlier discussion at #13), I see no reason it cannot work for complex matrices as well. Note that julia's sign function is indeed implemented for complex numbers, so the interface can be exactly equivalent to the current one.

EDIT: on the other hand, I believe logdet should only be implemented for real matrices, as is currently the case. OK, apparently logdet is implemented for some complex matrices.

Thoughts?

CC @mishmash

[jiahao]

Sure, I don't see why not. The only possible complication I foresee is propagating the branch cut of log properly.

[andreasnoack]

Fine with me. The changes required are minimal: just remove the restriction to real inputs and make the accumulator real by wrapping the T in a real.