positional parameters siganl repetition (a la vmstat)

[asdkant]

After raising the issue #24 I thought it'd be an easy thing to do, and did it. I tested it with both python 2 and 3.

[wookayin]

Thanks for your contribution. I was considering to use not positional arguments, but optional (keyword) arguments such as --watch, and it remains controversial in my mind.

And, I feel it is much easier to see what is changing if we use something like watch -n1 gpustat, as top or htop command does, rather than simply appending the output.

[asdkant]

Well, this IS a "(somethng)stat" command, so I just figured it'd be natural to follow the *stat convention