Easy3D-v2.0

Major changes:

• Reorganized the classes/functions in modules (i.e., core, viewer, fileio, util).
• Added a few rendering techniques (e.g., shadow, eye-dome lighting, ambient occlusion, transparency).
• Added a few tutorial examples.

Easy3D-v1.0

The first release of Easy3D tested on macOS, Linux (Ubuntu), and Windows.