Documentation folder structure + publication process

[Miles-Garnsey]

Summary

The documentation folder structure could be simplified, as currently ASCIIDoc components reside within manual/, while the published documentation resides within doc/.

This is probably to work around the fact that github.io (the documentation hosting mechanism) will only publish pages from the project root, or a folder called doc/.

Proposed changes

I suggest that we modify the documentation publication process, so that -

• The documentation is published out of the project root on a separate branch (which we'll call site-publish).
• Documentation sources reside within doc/.
• A branch called site-staging is created at every pull request to enable review.
• When a pull request is approved, site-staging is promoted to site-publish via Github actions (or CircleCI if preferred).