Log Message:
Update to 0.1.66

Changelog:
2019-06-12 babl-0.1.66
Added API call, babl_space_get_rgb_luminance,
Make most SIMD code-paths optional again on i686.

2019-05-25 babl-0.1.64
Support for Hygon Dhyana, and Y~aA formats for symmetric completeness.
Code consistency, gitlab CI, autotools and meson build improvements.