[feature request] customizable max value for legend

[依云]

The max legend currently is 230, so e.g. ping github.com shows all red for me because it's far away from here (China). Also sometimes I experience huge latency even to my router (>1s usually, today I have experienced >50s latency!). I want to tell those terrible times from bearable network lags.

Also I hope there are timestamps (e.g.) at the beginning of each line.