
   plot <x> <y> [-dx dx] [-dy dy] [+dx dx] [+dy dy]

   plot a pair of vectors.  the options allow for errorbars.  If only
   one of -dy or +dy is given, the given vector is used for the
   errorbar.  If both are given, -dy defines the lower errorbar, while
   +dy defines the upper errorbar.  This allows for assymetric errors
   in a trivial fashion.  The same applies to the -dx, +dx values.  

   The vectors are plotted with the current plot style.  See style for
   all of the options.


