Update/tune Advanced deck section, content, headings

Reorganizes a few topics and groups them into more unified headings. Removes topics yet to be explored/detailed in a manner applicable for Kit.
This feels like it could be a small part of a bigger section on "Navigating the Git Graph", alongside "Treeish & commitish" and the use of the relative commits like HEAD@{today} for [compares on the web UI](https://help.github.com/articles/comparing-commits-across-time).