fixed entry_points scripts for setup.py

ArgumentParser.parse_args takes arguments from sys.argv by default, so
by using args=None we can call maestro.__main__:main using setuptools
entry_points, creating a "maestro" executable instead of having to call
"python -m maestro", which is unnecessarily verbose and doesn't play
well with bash_completion
Merge pull request #28 from fcoelho/console-scripts

Fixed entry_points scripts for setup.py