Support for pathlib.Path

[raffaelemancuso]

docx.document.Document.add_picture should support pathlib.Path objects.

Currently it returns an error if you try to pass the file name of the image as a pathlib.Path.

[scanny]

Yeah, it was written in the days well before pathlib appeared in Python 3.4.

If you just do str(path) in your call that will work for both str and pathlib.Path paths.

But I'll have a look at adding this next time I'm in there :)