flexible uwsgitop

Hi mate,

I'd like to propose these modifications to add the following capability to uwsgitop :

* better command line options handling based on argparse
* -d option to let people set the refresh delay (like top)
* -n option to let people have a predefined number of iterations (like top)
* -b flag for batch-mode operation, without ncurses formatting/colors for home made processing (like top)
* socket path checking and cleaner exit
* automated help and version options

Tested with standalone and emperor stats, hope this comes handy.

Thanks !