Made PEP-8 compliant

Removed multiple imports in one line, 2 blank lines between function
declarations, splitted >80 chars line. Verified with pep8 checker
https://github.com/jcrocholl/pep8/
Made directory an mandatory argument

And not a mandatory "option"
Rationale:
http://docs.python.org/2.6/library/optparse.html#what-are-positional-arguments-for