Refernences to Appendix [A-C] in various places aren't clear

[jdm]

There are no such letters in the sidebar, only a "Appendix" chapter with named subchapters.

Seen in 3.0, 3.2, 5.0, and 11.1

[carols10cents]

Yeaahhhh I think nostarch started using letters for the appendix sections. I'm not sure how to handle this with mdbook.... if we change the headings so that they say, for example, "21.1 A. Keywords" would that be more or less confusing? :-/

[jdm]

That seems like a reasonable change to me.