Build developer documentation

[antond-weta]

We should look at setting up the building process for the developer documentation. We do have docstrings on all public APIs, just building something automatically from them would be a good start.

Suggested solution:

• set up doxygen / sphinx for automatic documentation generation

[InfraPlatformer]

I'll set up Doxygen + Sphinx for automated documentation generation. Since this is primarily C++ with recent nanobind additions, I'll:

• Configure Doxygen for the core C++ libraries
• Set up Sphinx with Breathe integration
• Create build targets in the existing CMake system
• Structure the docs to include both C++ and future Python APIs

[lgritz]

This is a great initiative! I would also recommend hosting the docs on readthedocs.org. Many of the other projects do this, and LF will also set up a vanity URL redirect for you. Here's what it looks like for OIIO (which also uses a Doxygen/xml + Sphinx + Breathe + Readthedocs pipeline):
https://docs.openimageio.org

[pmady]

Here is PR(#222) for build developer docs. Please let me know you comments/feedback