Linefeeds were originally used in the place of <p> tags to denote a paragraph. While much of the linefeed usage has been replaced over time, there were many places where it was still being used, especially in reference.xml. This made it difficult to get consistent formatting across different output types. In particular there were formatting issues in the command-line help because it is harder to audit than HTML or PDF.
Replace linefeed formatting with proper <p> tags to make formatting more consistent.
Remove double spaces in all text where <p> tags were added since it does not add churn.
Update all <ul>/<ol>/<li> tags to the more general <list>/<list-item> tags.
Add a few missing periods.
This is consistent with the way BackRest and BackRest test were renamed way back in 18fd2523.
More modules will be moving to pgBackRestDoc soon so renaming now reduces churn later.
