lilypondMFE: loop from -1 system

It has to loop from the first system because if there aren't any
headers in the file the example doesn't work.

If no headers should be printed in the example they should not
be included in the input file.
lilypondmfe: Fix argument number bug

This was preventing the function to work :-(
fancyref: Fix German default captions

it seems that one has to "renew" the German captions
because they have already been defined in the English section.

Fixes #4