In particular, this ensures they are in GPU memory when GPU rendering us being used.

Added built-in eta and k spectra for CuZn (brass)
Fixed some small bugs in --upgrade
Improve SampledWavelengths::ToString()
GPU: issue warning on unsupported options (--force-diffuse, etc.)

This isn't supported in 3.14.3, at least, but list INSERT with a 0 index is
equivalent and is available there.

(PR #73 followup)

CMake improvements

Mostly minor code motion and clang-format formatting.
RandomPermute4() is now gone, since it's no longer used, however...

Switch to a tabule of permutations -> 3x faster (!)
Use 64-bit indices to handle high res / high spp images better.

...and add a test that would have caught them.

Implementation of Ahmed and Wonka's "Screen-Space Blue-Noise Diffusion of
Monte Carlo Sampling Error via Hierarchical Ordering of Pixels" sampler
(http://abdallagafar.com/publications/zsampler/).

Final images were never being written(!)

The CPU integrators no longer write out WIP images during rendering by
default, but this functionality can be enabled using the new
--write-partial-images command-line flag.

Noted in issue #85.

Issue #84.

Fixes cmake policy CMP0077 build error on windows

(And then the RNG from there on out.)

Also added a bunch more point sets and input formats.
The radially averaged power spectrum is also output now.

"none", "cranleypatterson", and "owen" are now available.

And similarly for the "randomization" option for the Sobol' samplers.
Also, rename XORScrambler -> BinaryPermuteScrambler