Documentation overhaul for v2.0.0-beta

[TzuChieh]

General

• [ ] Add a release and update Blender addon doc (mention version 3.6+, install procedure)
• [ ] Add a terminology page
• [ ] SDL format guide (update from the old SDL tutorial)
• [ ] Feature overview
• [ ] Gallery
• [ ] Demo scene download

Use doxygen's @class command to add SDL docs

See https://www.doxygen.nl/manual/commands.html#cmdclass

• [ ] Add a doxygen mode to SDLGen and SDLGenCLI
• [ ] Output a .dox file containing documentation extracted from SDL definitions
• [ ] Add this .dox file to project doxygen.config or base config

Automatically generate SDL documentation from our SDL descriptions

Generating markdown might be a good choice.

• [x] Basic parameter information, description, etc.
• [ ] Parameter range
• [ ] Examples
• [ ] Maybe a doxygen-specific SDLGen mode, as some markdown syntax are different in doxygen. We can also add richer info using doxygen's format.