Document MeTTa and APIs

[vsbogd]

This issue is to discuss and track the status of the documentation of the MeTTa functions and APIs we have at the moment.

List of APIs we have with their status:

• MeTTa language tutorial - complete https://github.com/trueagi-io/metta-lang-dev
• MeTTa stdlib documentation - nothing, tracking issue: MeTTa libraries documentation #321
• Rust API documentation - complete
• Python API documentation - complete Python documentation #416
• C API documentation - almost complete

1. (?) The format of the MeTTa documentation is an open question. It should be a set of HTML pages which contain the language tutorial and a reference of the standard library.
2. Python code should be documented using docstrings.
3. C API is written in Rust and should be commented in Rust using documentation comments. These comments then will be converted to the C API comments using cbindgen tool. After that comments from the C header could be converted into C API docs using Doxygen.
4. Add a separate CMake command (doc) to generate the documentation for the project.

[luketpeterson]

I will take the C part of this task. However, is there a preferred style I should follow for the Doxygen comments?

[luketpeterson]

The C API docs are merged, and can be built with Doxygen 1.9.7. Next step is to get them published automatically and hosted on the web, which @wenwei-dev is taking care of.

[vsbogd]

https://metta-lang.dev and https://github.com/trueagi-io/metta-lang-dev solves the tutorial item

[vsbogd]

Python documentation is solved in #416