A big round of crate documentation and API doc generator improvements. It's becoming more viable to use as a real doc tool.

New crate documentation and examples - Added doc pages for axum, tower, hyper, http, ctrlc, termcolor, and tera.

API doc generator fixes - Getting the custom rustdoc renderer to behave as expected and/or similar to rustdoc is a slog. And our implementation has grown organically: fix one link, break another. Complicated by my insistence on rendering fewer duplicate pages that rustdoc, so deciding where the "real" docs live and routing links correctly is tough.