Update to FreeImage 3.16.0

“Release 3.16.0 brings two brand new plugins: a WebP plugin and a JPEG-XR plugin. It also provides better support for RAW, JPEG-2000, BMP, SGI, ICO, PSD, TIFF, TGA, GIF formats, as well as enhanced functions for JPEG lossless transformations. The rescale function is also slightly improved.
The library has been updated with the new ZLib (1.2.8), LibJPEG (9a), LibPNG (1.6.10), LibTIFF (4.0.3), LibRaw (0.16.0), OpenJPEG (2.1.0), LibWebP (0.4.0), LibJXR (1.1).”

It seems like we might want to start adding build options so you could e.g. `brew install freeimage --with-webp`, etc. rather than having to know which packages to install beforehand