Using the changes from @gadomski along with some additional work, to get the
generated bindings working again. Works on macOS and FreeBSD 11. A couple of
hacks are needed for FreeBSD, but nothing too serious.
Changed to use the libc prefix, and changed to use the generated enums.
Fixes#22, #15, and #14
cargo test passes
This method goes down to `MagickGetImagesBlob`, which allows for
creating animated gifs.
I didn't abstract out common operations between the two in the interest
of not overly polluting the codebase. However, this new method is almost
identical to `write_image_blob` so you could probably abstract something
out of there.
