[Feature Request] Add command line options to for a fixed Y axis scale

[Klaws--]

Currently, the Y axis (roundtrip time, milliseconds) is scaled dynamically, both minimum and maximum coordinates. That is, actually, pretty nice, but required reading of the Y coordinates to figure out how many milliseconds a "peak ping" took (or a look at the top line for the "max ping").

Proposal: a command line parameter, or two, to specify a fixed Y axis coordinate system.

Example:
gping google.com -min 8 -max 50
Minimum Y coordinate: 8 ms, maximum Y coordinate: 50 ms.
Naturally, if a plotted point exceeds these Y coordinates, the Y coordinate of the point must be capped to stay within the visible range (albeit at the minimum/maximum bottom/top location), so the user can determine whether pings got too slow or too fast (assuming pings can ever get too fast...).