1. User can set the "primary" branch to live at page root.
This is `publish` by default.
2. User can set a list of aliases (symbolic links).
The default setting maps `draft` to `main`, and `book` to `publish`.
3. User can set a list of branch to be deployed.
By default: deploy all branches (indicated by '*').
NOTE: If user wants no branches deployed, or no aliases, they can set
the corresponding variables to ' '.