Character encoding (Windows)

[Veldhoen]

Python uses default system character encoding in calls to open(..). Under my Windows installation, this is cp1252, causing 'annif loadvoc' to fail with encoding errors.
I created a pull request where I explicitly added the encoding (utf-8) in every call to open(..)

[osma]

Thanks for the issue report and the PR! Will look into this. I've only used Annif on Linux (using a UTF-8 locale) so haven't encountered this problem so far...