Apply @uobikiemukot's patch (various pixel-format support)
https://gist.github.com/uobikiemukot/7adab29310caf0be6f7a
Swap bytes if depth == 2
Keep compatibility
Merge pull request #8 from saitoha/fix-segfault-with-introducing-various-pixformat

Keep compatibility
@uobikiemukot's patch in the conversation of #8
Merge branch 'feature-support-various-pixformat' of github.com:saitoha/libsixel into feature-support-various-pixformat
Merge branch 'master' into feature-support-various-pixformat

Conflicts:
	converters/img2sixel.c
	include/sixel.h.in
	src/tosixel.c
Merge branch 'hotfix-preventing-double-free' into feature-support-various-pixformat
Merge branch 'feature-omit-palette-definition' into feature-optimize-data-size

Conflicts:
	src/tosixel.c
Add --palette-type option
Add new API sixel_output_set_palette_type
Merge branch 'build' into release-1.3
Support HLS palette
Update ChangeLog and NEWS
Merge branch 'release-1.3' into feature-libpng-integration
Fix segmentation fault on quitting GIF animation with -u option
Merge branch 'master' into release-1.2
Merge branch 'hotfix-fix-segfault-on-quit-animated-gif' into release-1.2
Update ChangeLog
Merge branch 'hotfix-fix-segfault-on-quit-animated-gif' into release-1.3