Speed up PDF generation and add timing debug output

... to the Doxygen generation log file `documentation/pdfall.log`.

The additions to the log file are intended to find out which parts
take how much time.

Note: use `grep "make_pdf" documentation/pdfall.log` to see the
  log output with timestamps.

- documentation/Doxyfile.in: exclude undocumented source files in
  src/xutf8/* which reduces parsing by a small amount of time,
  estimated about 5 percent of build time. YMMV.

0 files changed, 0 insertions, 0 deletions