Little CMS bindings for Rust

Makes LCMS C API available in Rust. There's also a higher-level wrapper.

It's up to date with version 2.8.

Differences from the C API

• Type names don't have the cms prefix, e.g. cmsColorSpace is ColorSpace.
  • All C function names remained the same (with the prefix, e.g. fn cmsReadTag()).
• Enum values don't have the cmsSig prefix, e.g. cmsSigLabData is LabData.
• Some arguments use more specific type, e.g. Intent::Perceptual enum instead of INTENT_PERCEPTUAL integer.