Switch to argparse

[Ayush1325]

I have kept any changes not directly related to argparse out of this PR. However, switching to it should allow a lot more code cleaning in the future.

[JelmerT]

This one was long overdue and a great improvement, thanks so much!

[git-developer]

The type change of port is incompatible to previous versions, see #161. What's the rationale behind this? The documentation was not updated.

[git-developer]

After looking at the code, I get the impression that this was not intended. The following types are set:

• len: int, had a number as default before => OK
• baud: int, had a number as default before => OK
• address: int, used device.flash_start_addr as default before which is a number => OK
• port: int, used as string in the code

Please confirm whether you regard #163 as a valid fix.

[JelmerT]

Thanks for the catch and fix @git-developer, I definitely didn't test this PR enough before it was pulled, my bad.
But at least now it's in there and being tested ;)