Plot label

Usage: plot label axis position [text]

labels the given axis by placing a tic and the text at the given position. The parameter axis can have the following values:

 x or bottom   Label the x-axis, i.e. the horizontal line at
               y-position Y0. 
 y or left     Label the y-axis, i.e. the vertical line at
               x-position X0.
 top           Label the horizontal line at y-position Y1.
 right         Label the vertical line at x-position X1.

If text is blank, only a tic is set.