Fixes encoding woes for windows.

This version always uses utf-8 as output encoding, allowing easier use
on platforms that use lacking default encodings.

Note that if only Python 3.4 would be supported, this could've easily been
done through the argparse.FileType's encoding parameter. Right now the
output_file_type function emulates the desired behavior in a non-generic
way.
Merge branch 'master' of github.com:utwente-db/eca