glTF dominance release

glTF-focused release of Three-rs:

• parent objects now hold children alive, not the other way around
• PBR materials, custom pipelines
• glTF scene loader, including animation curves
• animation framework with vertex skinning and morphing
• instanced rendering
• text objects
• skybox and background texture support
• richer input API
• gltf examples: PBR shader, node animations, morpth targets, vertex skinning

Refined release

Refined APIs and new capabilities in Three-rs:

• basic documentation
• Mint-flavored math API
• revamped input API, orbital camera controller
• blend shape animations
• optimized scene graph and renderer
• examples: anim, group (cube-ception)

Initial release

The first experimental version of Three-rs library, includes:

• scene graph built with Froggy
• renderer with gfx-rs
• shading models: Flat, Gouraud, Phong
• light source types: Ambient, Directional, Hemisphere, Point
• basic directional light shadows
• Wavefront OBJ loader
• texture loader
• examples: lights, materials, obj, shapes, sprite, basic aviator