Store sections by entire section hash.

Signed-off-by: Matthew Boedicker <mboedicker@pivotallabs.com>
[Finishes #69118480] Specifying versions in config.yml includes namespaced content from those versions

Signed-off-by: Matthew Boedicker <mboedicker@pivotallabs.com>
Improve user output when tagging.

Signed-off-by: Matthew Boedicker <mboedicker@pivotallabs.com>
Copy index files when publishing older versions of the book.

[#69118480]