Fix `-h/--help` in `karoo-gp.py`

[ezio-melotti]

Currently running karoo-gp.py starts the interactive mode without printing any help. This is because of this line:

karoo_gp/karoo-gp.py

Line 72 in 76613da

if len(sys.argv) < 3: # either no command line argument, or only a filename is provided

This should be refactored to use argparse from the start, and not just in the else to parse the cmd-line args.