Do a general refresh/revamp of `mdbook`

[anishnaik]

There are some pieces that we still need to document (testing API) and there are some pieces that have changed (how coverage is tracked).

[0xZRA]

@anishnaik If this issue doesn't have a hard deadline, I can start looking into it and would likely be able to complete it within the next few weeks. Let me know if that works.

[anishnaik]

Hey @0xZRA absolutely! Please feel free to take the charge. I can provide a lot more context on my "vision" on what I want it to look like. I will provide it here next week.

[0xZRA]

@anishnaik Would you like me to begin working on this task while you gather and share additional context information? In the meantime, I can jump on either issue #599 or #598?