Add support for Doxygen documentation

[meshtag]

Is your feature request related to a problem? Please describe.
There is no developer documentation for the project at the moment. We should add this as the project becomes more mature.

Describe the solution you'd like
We can potentially use Doxygen to generate developer documentation for us. You can also use cool extensions like this one to get documentation boilerplate while writing the code. Perhaps we can make a rule of including developer documentation in all new PRs which will be accepted?
(/cc @zhanghb97 @FlagerLee @MbjYjbpivj @xlinsist @SForeKeeper @Avimitin et al)

Describe alternatives you've considered
Feel free to suggest any other alternatives that you might like, but we should stick to one tool for the entire codebase.