Option object in JSON format. Possible attributes:
<br><br>
<b>marginTop</b>,
<b>marginRight</b>,
<b>marginBottom</b>,
<b>marginLeft</b>,<br>
<b>headerCenter</b>,
<b>headerLeft</b>,
<b>headerRight</b>,
<b>headerFontName</b>,
<b>headerFontSize</b>,<br>
<b>footerCenter</b>,
<b>footerLeft</b>,
<b>footerRight</b>,
<b>footerFontName</b>,
<b>footerFontSize</b><br>
<b>pageSize</b><br><br>
Please check out the
<a target="_blank" href="http://wkhtmltopdf.org/usage/wkhtmltopdf.txt">wkhtmltopdf documentation</a> for more info.