fix the behaviour of the primitives' style attribute:
fix the behaviour of the primitives' style attribute:

 - the default (undefined passed) is now "S" when in "simple" API mode
 - when "null" is passed, no operator is printed

yWorks/jsPDF,yWorks/jsPDF,MrRio/jsPDF,MrRio/jsPDF,yWorks/jsPDF,MrRio/jsPDF