Create Appveyor.yml script building libgd from source

This work is open-source. I'm doing extensive work with LibGD on Windows (x86 & x64), and I need to have continuous integration set up. Your mission is to create an [login to view URL] file that successfully builds libgd (both 32 and 64-bit), on windows, producing .dll files, and executing the included unit tests. I recently completed this for libwebp: [login to view URL] There are 2 forks of LibGD - the original (which I'm working with): [login to view URL] And the version included with PHP: [login to view URL] PHP has a guide to building on Windows (including LibGD). [login to view URL] I will accept either version building and testing properly on AppVeyor. The build should not include unnecessary software; it should only build LibGD and dependencies (or use precompiled dependencies from [login to view URL]). Two artifacts should be generated, .zip file for 32 bit and a .zip for 64 bit. If you need MinGW for any reason, you can 'cinst [login to view URL]' and 'cinst cmake', example: [login to view URL] You do not need to support libxpm; however, libjpeg, libpng, and Freetype support must be enabled. vpx/webp support is optional.