  plptex(x, y, dx, dy, just, text)
  ********************************

  plptex

  Writes text at a specified position and inclination within the viewport.
  Text is clipped at the viewport boundaries. The reference point of a string
  lies along a line passing through the string at half the height of a
  capital letter. The position of the reference point along this line is
  determined by just, the reference point is placed at world coordinates (x,
  y) within the viewport. The inclination of the string is specified in terms
  of differences of world coordinates making it easy to write text parallel
  to a line in a graph.

  x (PLFLT, input): x coordinate of reference point of string.

  y (PLFLT, input): y coordinate of reference point of string.

  dx (PLFLT, input): Together with dy, this specifies the inclination of
  the string. The baseline of the string is parallel to a line joining (x, y)
  to (x+dx, y+dy).

  dy (PLFLT, input): Together with dx, this specifies the inclination of
  the string.

  just (PLFLT, input): Specifies the position of the string relative to
  its reference point. If just=0, the reference point is at the left and if
  just=1, it is at the right of the string. Other values of just give
  intermediate justifications.

  text (char *, input): The string to be written out.

