conversation.py: Removes deprecated function.
Implements --restrict-file-names. Closes chfoo/wpull#62.
Saves filename to database to allow converter to work consistently.

Closes chfoo/wpull#45.
converter.py: Uses filename field instead of PathNamer.
database.py: Schema change: Adds filename field.
engine.py: set_status accepts kwargs.
processor.py: WebProcessor uses new root_path argument.
writer.py: save_document() returns filename.