Raise an exception if the config file contains options that we never
use, not even as optional ones.
Removed unnecessary 'vocabs' parameter from test_skll.py since it
was causing tests to fail.
Merge pull request #59 from EducationalTestingService/feature/warn_about_unknown_options

Raise an exception if the config file has any options we never use, not even as optional ones. Fixes #58.