Replace leftover instances of SrReal with Structure.
Use default sphinx theme with collapsible sidebar.

Let's consistently use the same theme as for Python documents.
Fancy themes could be good for a website project, but not for manual.
Authors fixed to use a common definition of actual package authors.
Use the current year.
Create local gh-pages before cloning to temp repo.

The "publish" target clones the local gh-pages branch for updating
HTML documents.  However, the local gh-pages may not exist in a fresh
clone from GitHub, which would only have remotes/origin/gh-pages.