Iris Shaders

This is a major bug fix release for Iris 1.8, fixing quite a few bugs:

• Shader packs are now able to disable the stars and sky
• VRAM usage has been improved on some shader packs
• A bug where packs would randomly fail to load with Distant Horizons has been fixed
• A bug where packs such as KappaPT would have light leaking has been fixed
• Block ID's are now unsigned excluding -1 (this may break a small amount of packs)
• New shadow programs have been added: shadow_cutout, shadow_translucent, shadow_entities, shadow_block, and shadow_solid
• Distant Horizons + Iris does not instantly crash your Mac (it still does not yet work correctly)