Update to 0.1.46

Changelog:
2018-04-10 babl-0.1.46
added extensions with more coverage for u32, half and other utilit fast paths
improving fast path coverage.

2018-02-18 babl-0.1.44
Fix bug in custom primaries/ICC fast paths, improve meson build<br/>

2018-01-23 babl-0.1.42
Fully initialize fishes when loading from cache. <br/>

2018-01-16 babl-0.1.40
Added format "CIE XYZ alpha" color model and formats.
New API babl_process_rows for reduced overhead in some scenarios; though bigger
gains seen also for regular babl_process with reimplemented branch-free
dispatch, and faster cbrt. Added meson build; being tested in parallel with
auotmake, Improved reference conversions for formats skipping some of models
components, Fixed gamma handling in indexed/palettized formats and improved
gamma precision consistenct in sse2 conversions.<br/>

2017-11-15 babl-0.1.38
Added format "CIE L float", a couple of protections against division by 0.0

2017-11-10 babl-0.1.36
Optimized customized primary aware code paths for CIE Lab<->RGB conversions,
improved accuracy of gamma approximations. New API babl_format_exists() for
checking validity of babl format name, crash proofing of cache handling and use
of environment variables.

2017-10-06 babl-0.1.34
Brown paper bag release, Fix indexed / custom primaries conflict, and re-export
a symbol used by old GEGL/GIMPs.

2017-10-03 babl-0.1.32
Added custom primaries and TRC support through ICC parsing, improved
float<->half performance, rewrite of all conversions functions to adhere to new
signature.

2017-07-15 babl-0.1.30
Thread stability for palette modes, stricter alpha preservation, now
cross-compilable on android.

2017-05-30 babl-0.1.28
Fast paths for Lav <-> Lch, release triggered by pending GIMP release.

2017-05-09 babl-0.1.26
Build and install HCY color space, platform independences fixes to fish cache.

2017-02-01 babl-0.1.24
Improvements to profile cache persistance, fast paths that improve actual GIMP
use on various precisions, use single precision constants for some more of CIE
computions.

2016-11-05 babl-0.1.22
Added cache of profiled conversions, added HCY color model, some precision and
performance updated for fast paths.

2016-11-05 babl-0.1.20
Fix run-time errors, leaks, and race conditions. Add conditional fast paths.

2016-06-13 babl-0.1.18
Bugfix: take alpha threshold in consideration when processing floats in SSE2.

2016-02-12 babl-0.1.16
Improvements to half float reference, SIMD, and fast-paths, and CIE float fast
paths; cleanups of fast path extensions.

(ryoon)