|rotate() rotates the page 90 degrees (clockwise). It must be
called before a call to page() if the rotation
of the page is to be changed. The top of the plot will be on the right
of the screen.
In GUI environments, the plot will always be upright on the screen and
the window frame will be resized to the correct aspect ratio. To make this
more intuitive, we have defined two macros that may be
used instead of calls to rotate():
LANDSCAPE is equivalent to rotate(0).
PORTRAIT is equivalent to rotate(1).