Bumps version to 0.17a1.
docs: Fixup features, adds info about stopping. Adds --help output.
url.py: Adds DemuxURLFilter.
Refactors WebProcessor to use DemuxURLFilter.
scraper.py: Adds DemuxDocumentScraper.
Refactors WebProcessor to use DemuxDocumentScraper.
procssor: Refactors WebProcessorSession to not need many arguments.
Adds factory.py.
app.py: Makes Builder use Factory.
database.py: Fixes leaking of imported objects into documentation.
changelog: Updates latest to 0.16.1
Fixes unit test factory_test.py using wrong unittest import.
Bumps version to 0.16.1.

Merge branch 'develop'

Conflicts:
	wpull/version.py