Read commandline arguments using argparse.

[idosch]

In previous version the command line arguments were read manually. Now, they are read using argparse (builtin module).

Also, file now passes PEP8 check (using Flake8).

You don't have to merge it, I simply think it's better that way. :P

Anyway, good job! :+1:

[idosch]

btw, I forgot to edit the README (as always). You can use this:

punchcard.py [-h] [-t TITLE] csv png