UPDATE: libavif 0.8.4

Here is an update to libavif 0.8.4.

## [0.8.4] - 2020-11-23

### Added
* YCgCo support (full-range only, wantehchang)
* Expose `maxThreads` to `avifDecoder`, add `--jobs` to `avifdec`
* Add `avifDecoderNthImageMaxExtent()` streaming helper function to determine future reads
* Create AVIF_VERSION_DEVEL, which allows for in-development changes to be detected during the build
* New avifResult values: `AVIF_RESULT_INVALID_ARGUMENT`, `AVIF_RESULT_NOT_IMPLEMENTED`

### Changed
* Read/write one of each type of colr box, as allowed in HEIF 6.5.5.1 Amendment 3 (also now supported in libheif)
* avifenc/avifdec: Now guesses input file format by header inspection instead of extension
* avifenc: Fix y4m/stdin corner cases when trying to detect a "single image" encode
* Add some protections against improperly using AVIF_ADD_IMAGE_FLAG_SINGLE
* imir transformation: Disambiguate all usages of "vertical" and "horizontal" across comments and tooling
* Print MC value when warning resetting to defaults (wantehchang)
* Fix grid image rows/cols parsing on invalid data
* Allow override of HAVE_POISON_SYSTEM_DIRECTORIES_WARNING (bnason-nf)
* Lots of comments clarifications in avif.h


Index: Makefile
===================================================================
RCS file: /home/cvs/ports/graphics/libavif/Makefile,v
retrieving revision 1.13
diff -u -p -u -p -r1.13 Makefile
--- Makefile 16 Nov 2020 21:43:08 -0000 1.13
+++ Makefile 4 Dec 2020 21:20:06 -0000
@@ -4,10 +4,10 @@ COMMENT= library for encoding and decodi

GH_ACCOUNT= AOMediaCodec
GH_PROJECT= libavif
-GH_TAGNAME= v0.8.3
+GH_TAGNAME= v0.8.4
CATEGORIES= graphics

-SHARED_LIBS= avif 3.1
+SHARED_LIBS= avif 3.2

HOMEPAGE= https://github.com/AOMediaCodec/libavif

Index: distinfo
===================================================================
RCS file: /home/cvs/ports/graphics/libavif/distinfo,v
retrieving revision 1.9
diff -u -p -u -p -r1.9 distinfo
--- distinfo 16 Nov 2020 21:43:08 -0000 1.9
+++ distinfo 4 Dec 2020 21:18:47 -0000
@@ -1,2 +1,2 @@
-SHA256 (libavif-0.8.3.tar.gz) = BSdyCkk6CM/NVsri/hDoxnQRLr8abhww04/KW7KlBLI=
-SIZE (libavif-0.8.3.tar.gz) = 2948213
+SHA256 (libavif-0.8.4.tar.gz) = EWtGqaSXxu8XjFoguRLYrAL4iNyMU35AtdFnAII6mxY=
+SIZE (libavif-0.8.4.tar.gz) = 2952844