* 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 'arakiken-sandbox' into sandbox