Misc: Use argparse

[Dietr1ch]

My take at #70.

I tried using black for formatting, but things are not in a great shape now, so I just tried to match the format on the lines I had to change.

This looks correct to me, but I haven't been able to run the converted model yet, so I can't verify. I was able to convert it just fine, but got some tensor dimension mismatch later.

[ggerganov]

Hi, thanks for contributing!
There is no need to add extra dependencies for such simple things, such as argument parsing.
The current way is good enough. It can be improved by adding comments and better help description, etc.

[leszekhanusz]

argparse is part of the Python standard library, so this PR does not add any new dependency.