Since I've had my fair share of complaining about the lack of documentation, it's time I did my part, hence this patch, which provides documentation for a good majority of the frontend library.
Several more items could be added, describing how AnalysisConsumer interacts with AnalysisManager would be the most important of those. For now, I put the greatest emphasis on checker registration.
What should this be expanded with? Is this document too large, maybe I should split it up? I haven't documented much so far, so I'd happily take any feedback.