labes and filenames for chapters and sections

[davidfarmer]

It is good if the files containing chapters and sections had a meaningful name,
instead of something like "chapter4.(tex or mbx)".

A reasonable approach is to put a LaTeX label on every chapter and section,
and use a version of that label for the filename. See the mbx files for some examples.

[oscarlevin]

Fair point. I had already used meaningful file names, but not every section had an internal label. I've fixed this now in case it makes future conversions easier.