A new gauge fixing algorithm which returns the rotation field.

[SaltyChiang]

I implemented a new over-relaxation gauge-fixing algorithm. The major difference between the new and the old implementations is we can obtain the rotation field now. Our workflow often requires this.

The rotation field $g(x)$ is defined as follows:
$$
U^\prime_\mu(x)=g(x)U_\mu(x)g^\dag(x+\hat{\mu})
$$

There are also some utility functions such as gaugeRotation and gaugeFixQuality which can be exposed in quda.h, I'll add them later.

[SaltyChiang]

I'm wondering if I should just override the old interface computeGaugeFixingOVRQuda or add a new interface function. Please let me know if you have any considerations.

I tested the performance and didn't see any significant performance regression compared to the old implementation. But more testing is definitely needed.

[maddyscientist]

@Jenkins test this please

[maddyscientist]

Thanks for this PR @SaltyChiang. I don't think there should be any performance change, so I think we could just replace the old interface with the new one.

Can you go ahead and make this change to your PR? I think you'll need to update the MILC interface code (milc_interface.cpp) since that code calls the older interface, but that should be an easy change.