* img2sixel.c: Use gdk-pixbuf and libcurl.
* build-gdkpixbuf.sh: Added.
this commit is imported from arakiken/libsixel.
https://bitbucket.org/arakiken/libsixel/commits/fda0bcab1ec2598bada3d102d8f0cf35d848f6ff
Merge branch 'travis' into configure-gdkpixbuf
Minor fix
Add missing include directive
Add detection for PSD file format
Add test for HDR format
Fix segfault when source image is GIF
Merge branch 'fix-segfault-when-loading-gif' into develop
Merge branch 'develop' into release-0.19
Update minor version
Update configure script
Merge branch 'release-0.19'
Update README
Merge branch 'develop'
Minor fix
Merge branch 'sandbox' into configure

Conflicts:
	configure.ac
Merge branch 'develop' into manpage
Update manpage of img2sixel
Merge branch 'arakiken-sandbox' into arakiken

Conflicts:
	converters/img2sixel.c
Merge branch 'develop' into arakiken