include PDFs from subdirs. symlink instead of copy. get rid of of hardcoded paths

Hallo Folgert,

I have made some minor changes to make your package run on my machine. The code now also indexes PDFs from subdirectories and links to them instead of making a copy. (I added a try/except block in `collect.py` because I ran into issues whenever paths were to long.)

Groetjes,
Arne