Sample Frame Resolution

[djarbz]

I would like to request a feature for a custom sample frame resolution.
If both are given, the frame must scaled to fit both dimensions.
If only one is given, then only that dimension is scaled and the aspect ratio remains for the other dimension.

We could use something like the grid parameter with 0 being auto.

ie. For 200px high and dynamic width would be the following.
--sample-size 0x200