Add glTF 2.0 loader

[onox]

Add a loader that can load .gltf files that follow the glTF 2.0 specification. Use json-ada for parsing JSON.

• [x] Update loader from 1.0.1 to 2.0 specification

Basic structure

• [x] Scenes
• [x] Nodes
• [ ] Cameras

3D objects

• [x] Meshes
• [ ] Textures
• [ ] Images
• [ ] Samplers

Data layout

• [x] Buffers
  • [x] Inline data as base64 encoded string instead of an URI
  • [x] External .bin files
• [x] Buffer views
• [x] Accessors
• [ ] ~~Binary glTF~~

Rendering

• [ ] Materials

[onox]

Depends on #3.