Changes to making packaging saner

- Using setup.py develop for testing, making sure packaging is working
- ss now can be used as a module as well as from the command line
- Moved calculate_hash's functionality into ss itself
- Removed comment headers
Updated tox.ini with available environments
Adding test to ensure ss can be executed as script
Fixed ss:main reference in setup.py: tests fail as expected
Using ss hard-coded in help message

This ensures the output obtained so we can use it
in our 'main' testing.
Replacing subprocess.check_output for canonical implementation

- Python 2.6 doesn't have subprocess.check_output
Using process.communicate() and calling ss without arguments
Accepting more than one return code

Different return code between linux/windows, don't know why
test_script_main() also ensuring stderr is what we expect
main() should receive no arguments