Add Finnish translation for title_by_author

This is a tricky one. Finnish doesn't have a structure for presenting that sort of information in a simple form like that. The current solution is a bit verbose, it actually says "%{title}, written by %{author}".

I considered "title - author", but that feels too inhuman :) So, for now, I think this'll be fine.
Merge pull request #11 from Darep/patch-1

Add Finnish translation for title_by_author