Books need Version information

[sethwoodworth]

❗ We need a stamp on outgoing books that lets us know the state of the git repo that built it.

⁉️ Ideally, we would be denoting the commit or tag of the requirement repos HTMLBook and asciidoctor-HTMLBook that we clone during travis build.

[eshellman]

Could you elaborate on what you mean by "state"?

[sethwoodworth]

By state, I mean being able to refer to a specific commit in the history of a repo. I want to be able to track any given epub back to the asciidoc source and travis config.

[eshellman]

we could do it the way pip does either version or full url

[sethwoodworth]

I wrote this up in our documentation on using semantic versioning. This can be done with the metadata _version key and a git tag. This would be good enough for now.

Later on we can do things like grabbing the git commit hash from the repo or even generating a checksum of the repo's contents. Ideally we would also maintain our own clones of the sources we use during build (like HTMLBook) and have a version number specified for each. But that can come later.