Draws a circle.
pdf_documentThe document handle, returned by cpdf_open().
x_coorThe x-coordinate of the center
y_coorThe y-coordinate of the center
radiusThe circle radius
modeThe optional parameter mode
determines the unit length. If it is 0 or omitted the default unit as specified
for the page is used. Otherwise the coordinates are measured in postscript
points disregarding the current unit.