Don't create temp dir in xml-to-pef.convert

Creating (and deleting) directory becomes responsibility of
caller (zedai-to-pef or dtbook-to-pef)
split-into-sections bugfix

For each section, copy over last occurences of `louis:print-page`,
`louis:running-header` and `louis:running-footer` from preceding
sections.
Add pef:validate (untested)