Gamut Compress v0.6

• Remove hexagonal mode. Inversion did not work as expected, and is non-trivial to fix. Hexagonal mode did a better job at preserving hues around primary colors, however it also introduced artifacts in smooth gradients due to the mach bands, and is more complex. The idea might be worth pursueing further, but needs more work to really make it useable.
• Change shadow rolloff default to 0.0. After more testing and discussion, having this feature disabled by default is more sensible. With it enabled, care had to be taken to ensure no important features with out of gamut colors in the image were below the shd_rolloff threshold value. If there were such features, the effect of the gamut compression would be reduced on them. In simple terms, the image had to be well exposed for problems not to ocurr. With shadow rolloff disabled by default, exposure invariance is preserved and the algorithm is more robust. I am not removing the feature entirely however, as it could still be useful. When exact inversion is required, the large distance values found in shadow grain can be problematic. Even setting a very low shadow rolloff value like 0.008 can dramatically help these differences.
• Bugfixes: There were some issues with negative color components not being preserved through the gamut compression which have been resolved.