Added output directory option

Fixes #3. When running `classify` a user can specify a (relative) path that will be used as the output directory. The behavior of `output_path()` is maintained, so if the user specified output path doesn't exist it will be created for them.

Usage to set an output path:

    classify --html --output /path/to/output/dir [-s [--django [ --django-settings [-p <port]]]] KLASS