Filepaths must be relative to the `Pygrobid/pygrobid` folder

[thundergolfer]

It appears that because the Java stuff is started from Pygrobid/pygrobid the file paths passed to the python library (which gets passed through by Py4J to Java) must be relative to this folder.

For example, there is a mypdffile.pdf in the Pygrobid/pygrobid folder, which is accessible by the filepath 'mypdffilepdf when you are in Pygrobid/ which the file path should really be pygrobid/mypdffile.pdf.

[thundergolfer]

Fixed by #6