add text stats to blip

[tarasglek]

blip is a useful tool, but it's hard to compare graphs across devices.
I added a div with text averages tarasglek@7aba781

I didn't submit a pull req because it's dirty

[apenwarr]

This is a neat idea. Another idea I was toying with was to draw a labeled horizontal line on the chart for the "average", and then additional lines for 2x and 3x the average, to show what happens in case of packet loss (typically 2 rtt instead of 1 rtt).

I haven't had a lot of time to work on blip lately though :)