Windows makefile and AppVeyor CI support
I've been working (along with several others) on creating a functional windows Makefile (windows\Makefile.vc).
We've also set up AppVeyor support so libgd can have (free!) windows continuous integration and automated binary releases.
Windows binary dependencies are versioned in a git repository, which is shallow cloned to a specific branch https://github.com/imazen/gd-win-dependencies
libjpeg-turbo, libpng, libiconv, and zlib support is enabled by default; libxpm and libvpx are not.
Currently 11 tests are failing for unknown reasons.
Among the required changes was the addition of a strcasecmp implementation to gdhelpers.c
I would really appreciate feedback and pull requests to get this feature into merge-worthy shape.