WIP: Some assorted updates

[bernhardschmidt]

Thanks for your code. It scratches quite an itch and I was about to write something on my own, but I'm glad I found your code.

I have whipped up a couple of changes. Unfortunately the changes are too large to make targeted pull requests. Documentation is still missing

Changes:

• Python3 compatibility, Python2 is untested
• move most hardcoded vars in the script into command line arguments
• support setting all command line arguments in a TOML config file
• calculate median using the statistics module, add stdev calculation
• make packet size configurable (we ping with 1000 bytes to make line errors show up sooner)

I will probably add some more, but in case I lose interest feel free to take parts (or all of it).