2PLOT: plot scale - scale a plot axis

Usage: plot scale <axis> <f1>... [exact]

List mode:
The command performs scaling of the given axis (x or y) on the basis of
the vector expressions f1,... Scaling sets the coordinates of the
reference points in the user coordinate system (X0 and X1 for the x-axis,
and Y0 and Y1 for the y-axis) such that they include all values of the
vector expressions f1,... If the option exact is present, then the
new coordinates of the reference points will correspond exactly to
the minimum and maximum of the vector expressions f1,...; otherwise a
small margin will be added in order to avoid that points lie exactly
on the boundary.
