Implement Gridlines

[MichaelM88]

I have not been able to find any way to add grid lines to my bar graph. I would like to add major grid lines and be able to set their color.

By the way I think all of these PHPOffice libraries are great. Keep up the good work.

[jqr108]

To add to this, I was wondering if there are plans to add other customization features to graphs (no markers and smooth lines on line graphs for example). And is there a way to change the color/thickness of line graph line?

And yeah, to echo @Vader88, baller library here. Keep on rocking Progi.

[Progi1984]

Link to #169 for Outline

[Progi1984]

@Vader88 : The documentation is here : http://phppresentation.readthedocs.org/en/develop/shapes_chart.html#axis