zaxis(title, ticks, proj) where proj=(x_z, y_z), draws a z-axis projected onto the paper plane by
  x' = x + x_z * z
  y' = y + y_z * z.
Optional argument labels specifies axis labels.
Optional arguments x and y specify the x and y intercept of the axis.
Optional argument lim specifies limits for the axis.
Optional argument below specifies ticks and labels go below rather than to the left.
Unlike xaxis and yaxis, zaxis cannot by itself find reasonable defaults for its main arguments.
zaxis supports textdist and ticklen, but not axshift.
Caution: positioning of zaxis titles may well change in a future version.