Updates to align with Project Gutenberg's current file structure

[tangledhelix]

The code to rebuild this data used out-of-date paths for the source material (12345-8.txt) where the files today are named 12345-0.txt. Because of that, and a number of other things (such as the pre-patches all having been fixed upstream), rebuilding the data no longer worked.

I fixed those issues, so that rebuild now works. The pre-patches were removed since they would no longer apply. There was also an issue with the 1973 and later volumes where the end of the book wasn't properly detected.

This PR should allow rebuilding the data (at least it worked on Debian/Ubuntu for me). I also rebuilt the data and committed that change (only one record was changed as a result).